Question on DIY plywood tank

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Feeder Fish
MFK Member
May 25, 2007
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Perth WA
In a few weeks I'm starting out on my plywood tank. It will be fiber glassed about 3mm thick.

The tank will be 10 foot in length 4 foot deep and about 4-5 foot wide. I have seen a lot of DIY tanks that have been extremely braced to stop any bowing out, now while I agree its better to be safe than sorry, from what I've seen and heard lately it may be that this is unnecessarily extreme.

The space I have in mind for the tank is rather limiting as its next to an entrance way, meaning I'm limited in the width of my tank, so of course adding to the thickness of the tank walls with thick bracing will lessen tank width even further.

I've been told of a technique where all that is required is to have a couple of ridges fiberglassed into the inside of the wall and this will negate any bowing out. This could be accomplished by using cardboard roll or pvc pipe for example and glassing over these.

Can anyone with experience enlighten me with what I should or should not have to do?

Thank you
 
You need to start with something non-flexible, what you've suggested will flex too much allowing the glass to crack in the joints or corners. Flexure is the enemy in fiberglas tanks (non-molded).

1200g - 1500g will be a lot of water pressure, even a small leak will cause delamination and lead to catastrophic failure if not repaired immediately.

If space is at a premium, have a metal frame (2" box) welded up that you can bolt together in place (no welding in the home). Properly designed this can be broken down and moved just by cutting the joints and re-glassing them at the new location. Steel that's properly rustproofed or a more expensive Stainless Steel option.

Don't skimp on bracing, it's just not worth the trouble.

Do you own your own home?

Dr Joe

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ill second that dont skimp on the braceing plywood and fibreglassing is a really strong way to build a plywood tank but they have to be properley braced as dr joe said if you let it flex the fibreglass will crack in the corners
 
Thanks for the response and advice. Yeh I have a friend who's an ex fitter and joiner who's taking on the build of the box. And thanks to a friend who recently left the trade I'm getting a cash job on the fiber glassing.

For the window side of things I was cutting them out of plywood, In what way do you think would be best to reinforce the windows? I may have side windows as well. Also is there a particular wall thickness I should use with the ply? I'm using 30mm acrylic glass to btw which is 8 foot long even though the intended length of the entire tank is 10.
 
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