center brace for plywood tank

[murph]

After some research I have decided the cheapest way to get the odd dimension tank I want is to build one out of plywood. I have even been able to to find some reasonably priced epoxy specifically made for aquarium and pond use.
Only problem I have with the designs I have found on the web is the six inch center brace which will pretty much be mandatory. Tank will be 54 long 19 high and 30 inches wide. I cant help but see this reducing light from my fixtures.
Question is if I could replace this center brace with piece of plexi that I could simply screw on top like a plywood brace and what dimensions could be used for this brace when using plexi.
Any input is appreciated.

 

[psusocr1]

IMO not the greatest idea although it could be done.. what you might get is the screws ripping out and pulling from the weight, i think it would really decrease the integrity of the structure.
what you might be able to do though is make a design in which you use a dado blade to dado the wood out and insert the plexi very flush and tight and then secure it from the outside as well so it wouldnt move, then epxoy around the bracing.. im not sure if you get what i mean buit hopefully you do

 

[murph]

Well I found another plan that includes another piece of plywood jigsawed out to provide a top for the tank similar to how acrylic tank tops are made. The center brace for this plan has just a four inch center brace which I think I can live with. The brace on my glass tank is 2 inch which causes no noticable showding effect so a four inch ply brace on the new tank cant be much worse.
I suspect having a single piece of plywood with cut outs on top of the tank will provide more stability than having just individual slats on sides and center anyway. Down side is it will add another 30 dollars to the project.
Thanks for the help.

 

[phixer]

A single sheet over the top with cutouts would be your best choice, it's less prone to bowing because the compression forces are distributed more evenly throughout the entire surface. Even with plywood make sure you use gruadual radius corners and not sharp 90 degree ones to prevent cracks from propagating.
If you use an acrylic strip as a cross member it will bow under this kind of load combined with a hot MH over it, if its too close the heat will cause the acyrlic to craze also. If the lights are too far away it kind of defeats the purpose. For this kind of design I would recommend placing your lights above the cut out sections only.