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Fiberglass tank


11 Oct 2009
Hi guys, I thought some one may be interested in a plywood & glassfibre tank I built quite recently.
My friend asked me if i could design & build a tank for his lounge - he wanted to keep blind cave fish but also wanted to keep live plants!
I built the tank ok but must apologise on my friends behalf because he never did plant the tank & it still lives in his shed waiting for the "right moment" :?

I have built lots of tanks in this fashion, some very large ones too but in this instance the tank was designed to fit a specific space, so I cut out the 18mm ply to suitable size.

I measured up the tanks location & decided on a 42" x 30" x 20" tank = 1070mm x 760mm x 510mm.
I was thinking along the lines of a 18" deep water level with some type of above water display, rock formation, tree root? Maybe a shelf just under the water level that will be heavily planted & a cave like appearance below the shelf!
I would make the background, shelf & maybe tree roots out of high density foam, in the foam I would make pockets for plants & LED lights.

Just thoughts at that stage but here is how the basic box was constructed.


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Blind Cave fish! I gave the issue some though & then got to work with shaping some foam to give the impression or rock coulombs .... I wanted to give the effect of caves & dark areas but with areas where the light could reach the plants....

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very interesting, never seen this before!!! whats making it waterproof? whats the fiberglass for? how did you attach the glass front? tell me, tell me now!!!!
Well one picture shows the application of the fiberglass mat being soaked with polyester resin, this give structural strength & then a more viscous covering of polyester gel coat makes the product waterproof & inert.
(Its the same stuff boats are made from & readily available)
The glass is simply stuck in with silicone.
I have made some interesting shapes in the past & tanks up to 2.4mt long using the method.
Brilliant idea. You could make tanks of any shape and design with that technique. 😀 Love the roots design work too. :clap:

I don't want to sound alarmist however, but being lucky enough to own a small river boat I know only too well that over time, fibreglass is not fully waterproof. Just type Gelcoat Osmosis into any search engine and you'll see what I mean. (Here's a particularly good write up of what happens http://www.yachtsnet.co.uk/osmosis.htm) I'd imagine that the resulting poly glycol filled blister could be pretty toxic to our aquatic chums if it burst. (I of course may well be wrong on this)

Admitedly, with a well made fibreglass hull this can take years to develop but may be something to consider if intending to keep a tank for a very long time.

Thanks Chris, fortunately osmosis is rarely encountered on modern boats.
What happens when water manages to find a way through the gelcoat, it can then wick its way into the fiberglass, this causes a dramatic increase in weight, causing the boat all sorts of problems!!
However on a small scale, the system is easy to manage & regulate but if one was paranoid, one could apply epoxy resin as a top coat.
The issue is more of a problem on a outdoor fish pond where water can reach the glass fibre from behind or in an open boat where rain water can travel into the glass fibre from the inside!
We're having our large (100' x 60') pond fibreglassed next week (weather permitting) and they're going to teach me how to do it.

Always fancied making a large 12' x 4 x 4' ply and fibreglass tank for the conservatory and using two sheets of acrylic for the front seperated by a bar halfway along.

Marine Batfish and other predetors, A large Arowana or a native coldwater tank would be my choices.
Big pond - small lake! please show some pictures.
You would need some thick acrylic for a tank that size probably 28 or 32mm but it would be a great choice for a cold water marine tank (my favourite).
You could insulate the tank with Double R & with the thick acrylic you should be able to run a relatively small 1hp cooler.
I built a similar tank for a sporting celebrity once!!