Glass Window verses Acrylic in a Plywood tank

Here is the now, I have a 750 gallon Plywood tank that has multiple layers of fiber glass resin on the wood then covered by two coats of sweetwater epoxy. I originally put two windows in this tank that are 2' x 4' of acrylic 1/2". When I put them in 3 years ago I used regular GE silicone and put stainless screws in every 8" to hold the window tight from the inside. After about 2 years one window began leaking between the silicone and the acrylic. I pulled the windows and using aquarium silicone I reset them but left a thicker layer of silicone between the window and tank by not tightening the screws as much. After about 8 months one window is now leaking in two places. The sealing surface is 1 1/2" all the way around the window. The water level is around 28" and the tank length on each side is 7.5' the window exposed is 21 x 45". The only other info is the tank is in a garage that is not heated and the leaks seem to happen when it is cold outside.

Now the debate, I need to replace and reseal these windows. Option one, replace with acrylic, buy a high dollar sealer that works better with acrylic, and band the window with 1" wide stainless flat bar to support the full edge of window. Cost for this is around $260.

Option two, replace these window with 1/2" plate glass and use regular aquarium silicone. Cost is around $280

Which option should I do?

M1A1 said:

You're losing a battle against the different thermal expansions of many different materials - plywood, fiberglass, epoxy, acrylic, silicone, stainless steel and water.

What temperature do you keep the tank at and what temperature does your garage get down to when it is 'cold outside'?

Click to expand...

In the winter the tank water is 76 degrees and the garage can see whatever is outside sometimes single digits. Right now it is low 30s and it is leaking. When it was 50 degrees the other day it was not. It did survive two winters with no leaks with acrylic, I wonder since the acrylic is older that it may have bowed enough to not go back to it's original shape. When I took them out and resealed they had about a 2" bow in them. The bow was towards the tank not outward so I am thinking the extreme low temps is causing the acrylic to suck in against the water which in turn is pulling it away from seal. My thought is glass will not expand and contract as much as acrylic does so it may be the best bet.

This pic is actually inside tank. You can see the screws and the water leak which is actually on the outside but looks like it is on side pic was taken. The seal is 1 1/2" wide and leak is at the top about 3" under surface.



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This is other window from the outside with no leaks. Windows are not recessed just laid flat on top of the side wall.



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