Aquariums

If your aquarium / master-piece-of-engineering ruins the living room carpet and your “someone special” has just exploded, now you can point to this photo and explain that it wasn’t your fault.

(You must admit, I do have that guilty look, so it should be easy.)

Now, if you really are considering building your own aquarium, I cannot emphasis enough the need to get the engineering right, because a dud fish tank will make a hell of a mess on your living room floor if you don't.

The other minor detail is the weight of water. Water is vvvery heavy.

(The average 4 foot aquarium weighs more than your mother-in-law and it will not only be her that breaks your heart, if you under-estimate the weight of your fish tank.)

A litre (around 2 pints) of water weighs one kilogram (about 2 pounds) and only takes up a space of about 4 inches high, 4 inches wide and 4 inches deep, that is 100 x 100 x 100 millimetres.

You only have to double ONE of these to double the weight. If you double 2 of these it is 4 times the weight and if you double ALL of them, it is 8 times heavier,....So 200 mm x 200 mm x 200 mm (just under 8 x 8 x 8 inches) weighs 8 kilos or nearly 20 pounds on the old scale.

....Here is a tank 1 metre long (about 3 feet) by 300 mm (1 foot) by 300 mm and when full of water, it weighs 90 kilograms, about the weight of a large man.

Now lets look at the same length tank, only 600 mm by 600 mm (2 feet x 2 feet and 3 ft long). It is 4 times heavier.

Yes, that's right, it weighs as much as 4 men. Now let's say, you decide you want a BIG tank, like, say, something about the size of a small car. At 2.5metres long and about chest high (that's about 4 foot 6 inches on the old scale) this monster would weigh over 6 tons or nearly 10 times MORE than a small car.

(BUT it would look great in your living room.)

Broadly speaking, engineering is the critical factor, not the thickness of the glass.

With enough braces you could theoretically build an enormous glass tank from very thin material, but it would not look very attractive. You would need to have vertical braces every few inches and that definitely is not what you want.

In order to get a reasonable viewing area, we need to consider thickness and the type of material for the job.

To start consider the following types.

Annealed glass

Laminated glass

Toughened glass

Polycarbonate and other plastics

Fibreglass with glass front and variations.

Annealed Glass

There are 3 types of glass commonly available that are used in aquariums, or more correctly one type that has been processed to produce different qualities. It is important that you understand these differences before you select (or more interestingly) try to cut it.

You will be familiar with all three but I will explain their normal applications and you will understand which will suit your task.

Most glass is produced as "annealed" glass. Also known as "plate" glass, "sheet" glass and other local names. When glass is in this state, it breaks into large chunks and slivers with razor sharp edges.

Lets nominate the strength of 6mm (quarter inch) annealed glass on a scale of 1 to 30 as a 10.

Laminated glass

The first common treatment for annealed glass is to laminate it to another piece of the same thickness.

It is common to laminate that is, join together, 2 by 3mm pieces to get a thickness of 6.38mm (the extra .38 being the plastic interlayer).

This new piece of annealed glass we now have is still approximately 6mm thick but on the same scale of strength, it is an 8.

While it suffers slightly in the strength department, the advantage of this glass is that if it breaks, no large dangerous chunks are falling about to slash arteries and lop off limbs. It is widely used in doors, low level glazing and anywhere that human impact could be a possibility.

Toughened glass

The other common treatment is to take the original 6mm piece and subject it to heat and a fast cooling job. This has the effect of "toughening" the glass and its strength climbs to an incredible 30 on our scale. Also known as "tempered" glass, best we use that type for our tank?

Well maybe, but I haven't told you the down side. When this glass breaks, there will be no small, leak, no crack letting out water slowly. When toughened glass breaks, it shatters into millions of pieces and occasionally, it will simply do that without any help from a brick.

If you have read my tutorial on glass cutting, you will know that glass is not "cut" but has a trench of weakened area crushed into its surface and pulled apart.

This is the other big drawback of toughened glass. You can't cut it. If you try to score a trench into its very hard surface you will end up with a lot more pieces on the table than you wanted.

Polycarbonate

What about polycarbonate (or Lexen or Plexiglass or one of the other brand names for polycarbonate)? The short answer is yes, you can use them, just as they do in tourist marine applications all over the world. (Popular in jails and police stations too.)

Like the glass though, it also has drawbacks, the main ones being, sufficient thickness and availability at a modest price, it is easily scratched and is harder to join and seal

Fibreglass

Yes, it is not uncommon to see large tanks that only require one face to be exposed, substitute other materials for the bottom, back and sides. So a combination of glass and a fibreglass box just might be your solution, however this tutorial does not cover the art of fibreglass work and ensuring that the surface of the fibreglass does not do strange things to your fish. (This is being addressed in another tutorial on advanced and multifaceted tanks still being developed. Watch this space, as they say).

Now to the task

We will assume that for this project that you are building the standard rectangular glass aquarium and proceed on the basis that you have or are going to source glass for the job.

You might buy new glass, however if you have inherited some or are planning getting it from a demolition yard, you need to check that it will be suitable.

For a start, check that it is not tempered glass. It can usually be recognised by either an etch mark in one corner, or more rarely, small indentations along one edge. (Early tempering was done by hanging the glass from tongs on a conveyor which took the glass into the oven.)

If you have 2 pieces the same size and it is tempered, you can still use it but whatever size it is, that is the size of your tank. You will have to get the bottom and ends cut to suit.

If it is laminated glass, it doesn't prevent you from using it, but be mindful of its relative weakness compared to the same thickness of a single thickness.

There is even an argument for preferring laminated glass in that very thick laminate off-cuts are often cheaply available from glass shops in small sizes left over from large shop front replacements.

The other argument for laminated is that if a crack occurs, you sometimes have more time to find alternative accommodation for the fish.

The last thing is obvious. Avoid heavily scratched glass.

Glass cutting

If you are keen to do the entire job yourself and cut and edgework your own glass, I suggest that you read my tutorial on glass cutting, as questions that may arise from this tutorial will hopefully be answered in The secret.

Engineering

This is where you make or break your aquarium.

I am repeating myself, but let me make this clear before we go on.

Broadly speaking, engineering is the critical factor, not the thickness of the glass.

These are the answers to 90% of the email questions I receive.

YOU DO NOT need angle iron bracing,

the silicone WILL HOLD the tank together,

YES, YOU DO HAVE TO have the braces

no, I CAN'T TELL YOU how thick the glass has to be.

The answers are here on the page, so read on.

The single most important engineering bits are the braces that support the long sides of the tank and the cross brace between.

All but the smallest tanks need horizontal (longitudinal) braces along the top edge of the sides to provide resistance to bending or "bowing" of the glass.

These are reinforced by a cross brace to tie the tops of the two sides together, and are critical for nearly all tanks.

 The Longitudinal Braces.

The braces should be glass of the same thickness as the sides and be of these dimensions. The length of the brace should be 90 percent of the tank length with a width 5 percent of the tank length. This means that a 3 foot tank (900 mm) should have braces approx 800 mm long by 45mm wide and (probably) 6mm thick.

A 5 foot tank (1500mm) would have braces of 1350 to 1400 long by approximately 75mm wide and probably 10mm thick to match the thickness of the sides.

The Cross Braces

Cross braces should be fitted "by the square" method, which roughly says that the surface water area should be boxed into roughly squares.

Looking down onto the top of a 6 foot tank (1800 mm long and 600 mm front to back) this would mean fitting 2 cross braces giving 3 "squares" of water surface approx 600mm x 600mm each.

Of course if the front to back is only 500mm the "squares" are actually 500mm x 600mm, but close enough for the formula. A 1200 mm tank would only have 1 cross brace making 2 "squares" of 600 x 600

These formulae are only guides, but I would not stray too far away from these dimensions, especially should the distance from front to back be more than 25 percent of the length.

The Base

There is a popular theory that the base must be very thick as it "carries all the weight". This is not the case provided the base upon which the tank will rest, is flat and strong. We will address the requirements of the foundations later.

Water Height and Glass thickness.

NOTE !!! THE GLASS THICKNESS DEPENDS ON THE HEIGHT, NOT THE LENGTH.

In determining the dimensions and glass thickness of your aquarium, particular attention must be paid to the height of the water.

The pressure on the joins where the sides meet the base increases dramatically with height. If you keep the height to the lowest acceptable, you will reduce the risk of a blow out. This does not mean you cannot have a tall tank, but it does create extra engineering problems.

As a guide, I recommend the water height should be no more than 500 mm for 6mm glass,

600 mm for 8mm thick glass,

700mm for 10mm etc.

As you will probably fill the tank to within 50mm of the top, this still provides for a fairly tall tank with no special requirements.

If you are planning a tall tank, say over 700mm, (30") the main things to check thoroughly are glass thickness, cover strips for the corners, and extra bracing where the base meets the sides.

At the end of this tutorial there is a section on the tank stand and you should look at making the stand with extra support on the sides to cope with the high water pressure that comes with having a tall tank.

AGAIN!!! THE GLASS THICKNESS DEPENDS ON THE HEIGHT, NOT THE LENGTH because you will be fitting bracing to the length to take care of the sides bowing out.

Cutting list

The thickness of the glass affects the cutting list sizes, so let us assume we are constructing a 4 foot rectangular tank, of 1200 length, 500mm height and 400 front to back, from 10mm glass.

(I hesitate to use the word depth, the way it is used in cabinet making and joinery, where it means the distance "front to back". In aquarium building, depth is often confused with height so I tend to use the phrase "front to back" to avoid ambiguity.)

As there are two common assembly methods, I suggest that the cutting be done in a way that will suit both methods of construction. More on the construction part later.

Now, to start cutting......

The Long Sides

The long sides (the front and the back) are the full length of the tank, in this case 1200 mm and the height is the full height of the tank in this case 500 mm.

The Base

The base will be shorter by the thickness of the ends, which, if we are using 10mm thick glass you deduct 20mm, or if using 6mm glass you deduct 12mm to allow for the 2 end pieces. As the base sits in between the sides and the ends, it is less than the full length of the tank.

The Ends

The ends will be the same height as the sides at 500mm and the same width as the base front to back measurement, ie 400mm less the thickness of the sides. So the ends will be 500mm high by 380mm (if using 10mm glass) for the front and back and our tank's finished size will be 400mm.

So remember, sides and ends are all the same height.

The sides are the full width of the tank.

The base is full size less the two glass thickness off both dimensions.

The ends are the full height and the same width as the base.

You can now cut the glass required for the tank using these formulae applying them to the glass thickness and dimensions for your plan. Before using the glass you have cut, make sure that all edges have been well sanded.

Care should be taken to "strengthen" the glass by eliminating microscopic "starts" on the edges and of course make handling safer. Do not wait until the tank has been assembled to complete this chore.

Assembly

Method one

This is the easiest assembly and the strongest, but not the neatest. If you are making tanks for resale, you will need to consider both methods.

Place some newspaper on a flat hard surface (not on a blanket or other giving surface) and tape the tank together.

This method is quick and reliable and most proponents assemble tanks with adhesive tape first and just run a bead of silicone around all the inside joins, then immediately run their finger over the silicone to make a curved join just where the pieces of glass touch.

This in not quite as neat as an accurate amount of silicone neatly and quickly applied in a tank assembly jig in a large factory, but it is stronger. Much stronger, because the silicone has a grip on a larger surface area.

While you are applying the tape, you can insert 8 very thin spacers between the glass, (2 on each height) however this is not vital.

On tanks 4 foot and less, it is totally unnecessary.

Spacers should be no more than 1.5mm thick (1/16^th of an inch on the old fashioned scale) and removed by your helper as you apply the silicone.

You should take your time to tape the tank together, to ensure that you are happy with how square it is, and that the panels line up correctly. If you have fitted some spacers, make sure you can remove them easily as you apply the silicone. Once you apply the silicone, it will be too late to change, so double check.

If you are building a large tank, you will need help. You may also need more than one tube of silicone, and as this is a time-critical operation, have the next one ready to go if you need it.

Applying the silicone

Cut the tube so that a solid 4mm of silicone comes out the nozzle, and, standing on the table or floor next to the tank, squeeze a continuous bead of silicone around the base.

If you have used spacers, have your helper remove the spacers as you come to them.

Now do the same to each of the verticals and then gently run your finger into the silicone to make it concave.

When you do this, some will get squeezed between the panels to add to the strength of the joins whether you have used spacers or not.

The secret is to do ALL the joins at the same time, preferably within about 2 minutes. This is very important as wet silicone does not like sticking to dry silicone.

While the silicone is setting, you are ready for cutting the braces.

Method two

This is the method that people go to instinctively, but is more difficult to get a good result.

The concept it to lay the tank out on a large flat area, usually the floor with the base in the centre and the sides and ends lying on the floor near to where they will be stood up.

Construction starts by running a bead of silicone on the bottom edge and both verticals of the sides. The sides are then stood up to embrace the end panels s and clips or tape is used to secure the whole assembly.

At this point it is important to promptly apply silicone to the inside of aluminium angle and place them over the 4 corners. This improves the strength of the tank to a very large degree.

If you have applied a neat, consistent line of silicone to the edges, the amount squeezed to the inside of the tank will be an even amount all along the joins.

A hybrid method, which I favour for large tanks, is to assemble as described, and then run another bead around the base inside, concaving the silicone with the judicious use of an index finger.

This tends to overcome objections to the lower strength around the critical area of the joins between the sides and the base using method two.

The single biggest drawback with method two is getting the right amount of silicone in a straight line on the edge of the glass before assembly.

Both methods are successful if done as described and without allowing the silicone to "go off" during the job.

Cutting and fitting the braces

This is by far the most important part of making an aquarium and you have a few hours to cut and arriss the braces while the tank is drying.

For the tank in our example, you will need 2 longitudinal braces about 1100 x 50.

The easiest way is to cut 1 piece at 1100 x 100mm and then split it down the middle.

The cross brace should be about twice as wide as the long braces (100mm) and cut to a little less than the front-to- back measurement.

So, depending on the glass you have available, you could cut a piece 1475 by 100, cut off 375 for the cross brace and split the other one to get the 2 long braces 1100 by 50mm.

Whatever way you go, remember the cross brace should be just a little shorter than the front-to-back measurement, so in our example 375 instead of the full 380 of the ends.

If you have arrissed the braces and at least several hours have elapsed, mark the OUTSIDE of the glass with a felt pen about 30mm from the top near each end and then, lay it on one side.

You should be able to see the marks through the glass and this is where the long brace will go.

Place the brace just inside the top of the tank using the marks to get the right position. Run a bead of silicone onto the inside of the tank side, using the edge of the brace as a guide.

Now stand the brace up on its edge and into the silicone.

Obviously you will now have to leave the tank again for a few more hours for the silicone to set. If you are really impatient, you can tape it into position after half an hour, being careful not to move it.

Then repeat the procedure for the other side.

After doing both side braces, the only thing left to do is place the cross brace on the long braces. This is achieved by "gluing" the cross brace or braces onto the long braces.

Just a suggestion, the cross brace should be about 5 to 10 mm less than the back to front measurement to allow clearance for the dried silicone along the edge of the long side braces. If you make the cross brace the full front to back internal size, it makes it hard to fit and makes no difference to the strength.

Put plenty of silicone on the areas of the side braces where the cross brace is going to go, so that it squishes out and covers the whole area where they join. If you are measly with the silicone here, you will see it through the glass and it looks a bit daggy.

You can clean up after it dries with a razor blade.

Silicone types

Manufacturers have 2 common ways of curing (dry to touch) silicone, non-acetic (neutral cure) and acetic cure. I prefer the acetic cure of Dow Corning 480 clear silicone, because I have never had an adhesion failure and never had a fish die.

(The popular myth is that if you use an acid cure the fish will die. I say, wash the tank out before you use it.)

The other interesting note about this particular silicone is that it says on the instructions that it is NOT suitable for aquariums.
This may seem strange but it works and has done for many years. I have never had a fish die or ever heard of anyone having a problem.
The Australian distributors told me that the aquarium market is minuscule but everyone blames the silicone if the tank fails.
It is not in their interest to acknowledge that it is suitable for aquariums when they have to put up with dimwits blaming them for leaks and the resultant damage.
As I said, I would not use anything else, but that does not mean that other products like Selleys would not do the job. In fact I think most would be OK, but I cannot recommend them as I have never tested them.

Corner covers

If you have used method one corner covers are a bit of overkill if we are considering just the strength of the tank. Its like the difference between being run over by a 5 ton truck as opposed to a 10 ton truck.

Just the same, the corner covers protect the glass against accident damage by collision and cover the silicone job if it is less than perfect.

So, even if you have used method one, corner covers are generally a good idea.

As a matter of interest, I once built a 12 foot tank weighing nearly 1 and a half tons using silicone only, no end caps at all, and never lost a drop in 3 years.

The aquarium display stand

While exercising your self-control and waiting a few days before filling the tank, we have time to consider the display stand.

While it may seem obvious, check first that the tank is standing on a sturdy base. The base must be able to stay flat under the pressure of the weight of the water. If the stand is made of metal or timber it must have enough supports to ensure it does not sag even a little in the middle.

The glass base may tolerate a little bend, the join where it meets the side, certainly will not.

There are many types of display stands and it is beyond the scope of this tutorial to describe them and suggest ways to build them.

In principle though, it is better to have support in the middle if possible if the tank will be over 4 foot long.

Before filling the tank, place a compressible material on the base of the stand to take up any small defects. A common material used is white polystyrene like that used in packing and foam coffee cups. Other materials like carpet will work, however can cause problems later if you have a spill.

I strongly recommend that when building the base that you make the base area exactly the same size as the tank and then fit a "lip" or "upstand" around the base so that the tank "drops in" to the base. This will provide extra support for the long sides of the tank at the critical area, where it joins the base and is under the most pressure.

The drawing only shows one side but you get the idea. The last one of these I did, I used construction adhesive between the support and the base of the stand. This, together with some long wood screws provides an excellent support against the water pressure trying to force the sides of the tank away from the base, but it must be a tight fit. If you find there is a gap between the glass and the support, (less than 3mm 1/8") you can overcome this with an acrylic gap filler from your hardware store. While it is compressible, and ideally it would not be, it has the advantage of being able to clean up with water to get a great finish and will have enough consistency to do the job so long as the gap is not too wide.

Filling the tank

We usually half fill larger tanks after 48 hours and give it a good wash out. A light detergent will remove any chemical residue from the silicone and a second wash will rinse traces of the detergent.

Now you are ready to fill the tank and delve into the joys of looking after your Piscean charges.

But that's another story.