1,000ish gallon Koi pond-arium ply tank...

  • We are currently upgrading MFK. thanks! -neo
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seraph

Feeder Fish
MFK Member
Dec 21, 2009
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Glen Ellyn, IL
Hey guys, after picking your brains for months and reading through ply tank builds and learning sketchup8, with the wife's blessing, my first ply tank should be underway shortly, but first, wanted to get some advice on my design.

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pond3.png


the measurements will be 9' L x 4' h x 3.5-4' d with a 30" tall viewing window

reason for the dimensions and design is, I have a 4'x8' sheet of 1" acrylic sitting in the garage that i got for free. At one inch, 30" is the max depth according to some calculators. Since a sheet this size is a once in a life time freebie, I have no desire to cut it down unless it is to make 1 19'L x 2.5'H x 3-4'D aquarium or 2 9 footers later on should i need to disassemble the pond

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or a narrower tank with 2 viewing windows...

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anywho...the plan is to go with the first design. the plan for water proofing is a 2 part brush applied or hopper sprayed polyurea called styrospray 1000 2 part polyurea coating which only cures when exposed to moisture in the atmosphere, it will not cure inside a spray gun or closed storage container for several days, you may apply successive coats every 30 to 40 minutes. 2 gallon system costs $120 and covers 150 sqft

They had sent me a sample applied to styrofoam and it is very rigid but flexible and a sample on brushed onto plywood and it has a death grip on the wood. I'll be getting a 2 quart system for $30 just to try it on some plexi to see how it adheres to it.

so...before i dive in, just wondering what you guys thinking about the design? There will be bracing on top, just didn't sketch it in yet. is it overkill? I'm just worried about 4 feet of water pressure.

any suggestions on acrylic install? i read some people did a bead of silicon all the way around (obviously sand and rough up the acrylic edge for better adhesion), let it cure before install to form a hard gasket and then siliconed it into place and even though silicone and acrylic are not ideal, the water pressure was enough to hold the window in place? others used dow product but i'm not familiar with it. how about Great Stuff Pond foam? Also, is a 2" boarder enough?

Thanks guys!
 
In the top design, are those 2x4's you're planning to use for construction? Also, what is the thickness on the plywood?
 
they are 2x4's that will be glued and screwed, the ply will be either 1/2" or 3/4" i'm leaning toward the 3/4ths for the extra peace of mind, unless it is not needed...
 
i wouldn't just glue in the acrylic panes. i would make grooves for the acrylic to slide in to give it extra support and to help prevent leakage. if u decide to do this make sure that the groove is big enough to allow the proper amount of silicon between the acrylic and what ever is going to be supporting the panes. if u don't understand what i am saying just ask and i can explain in greater detail or draw something up and post it. just remember that four foot depth is a lot of water pressure on those bottom seems make sure you do those right the first time.
 
the first row of lumber is actually a 2x6 so that there is ledge for the acrylic and plywood to stand on. i left a gap on bother sides for extra silicone or other adhesive product to fill in the sides.

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maybe even sandwich the acrylic after the gap is filled with 1" trip and the polyurea will do over the 1" and onto the acrylic 1"
 
Are you willing to consider a third option? If it were me I'd cross cut the acrylic into three pieces at 48" x 30" and build a tank with three front windows. Depending on the girth of the framing between the windows, maybe 14' long or so? Or you could do two windows on the front and one on one end.

Do you know if the quality of the acrylic is decent? There is some imported cell cast acrylic that is said to be pretty lousy. Bad enough that you wouldn't want to use 1" thick acrylic with anything more than a 24" water depth.

I believe Dow 795 has a matching primer that allows for a more secure bond with acrylic. It's been used in other MFK builds. Of course the silicone would still need to stick to the polyurea. Silicone does not bond to "regular" polyurea but the stuff you posted can be painted so it may not have the typical low surface energy of regular polyurea.

I'd also consider finding a caulk that you can use to seal the acrylic to your wood frame and then bridge over that with the polyurea. Both single and two-part polyurethane caulks as well as butyl rubber caulks may work and have been used in aquaria in the past.

When you get that two quart system you might do a test run on a small plywood box. Maybe even a tall plywood column so you can test the water proofing ability of it at the depths of your monster tank.

Of course two quarts will cover a lot so maybe even build a small sump or something else that will be useful to you.
 
the fist design is what i'm going with because of the placement and room available for the tank. the 19 footer is an idea if we move and have the room for it, then the 4x8 can be cut into 2 2x8's...i would hate to cut 30x96 and have a useless 18x96 left over...

the side windows are not needed any if the wife was to force me to put a side window, the spots in the house where it might go is in a corner, so only one side window if forced, but again, it would be a shame to chop this sheet up.

If it is low quality acrylic, i have no problem shorting the window up to 24", but the wife insists on the large view, and if it is low quality, i'm thinking that by having a 18-24" bottom boarder will increase the over all strength of the acrylic or is that not necessarily the case?
 
seraph said:
the fist design is what i'm going with because of the placement and room available for the tank. the 19 footer is an idea if we move and have the room for it, then the 4x8 can be cut into 2 2x8's...i would hate to cut 30x96 and have a useless 18x96 left over...

the side windows are not needed any if the wife was to force me to put a side window, the spots in the house where it might go is in a corner, so only one side window if forced, but again, it would be a shame to chop this sheet up.

If it is low quality acrylic, i have no problem shorting the window up to 24", but the wife insists on the large view, and if it is low quality, i'm thinking that by having a 18-24" bottom boarder will increase the over all strength of the acrylic or is that not necessarily the case?
Click to expand...

You wouldn't have 18" left over. In fact if you could cut three pieces at 32" x 48" and have zero waste. 96" divided by 3 = 32". Technically you'd have to subtract 2x the blade kerf as well. I don't know where you're getting the 18" waste from. I'm not talking about ripping the sheet but cross cutting (across the 48" width).

You could then build your current design or any other design and still have the option of taking it apart when you moved. In fact I think it would be easier.

Hope this makes sense. Your idea works fine too and leaves you with a full sheet of acrylic if you ever tear down. Nothing wrong with that.
 
Just wanted to clarify my preference for cross cutting is because of viewing area. With your first design you get 8' of viewing at the 30" max height. The reason why I would personally cross cut it is because you get 12' of viewing at 30" max height.

Of course this all assumes the acrylic is a moderate quality cell cast acrylic.

If 24" were to end up being the max depth then ripping lengthwise or cross cutting widthwise wouldn't matter.
 
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