Plywood Tanks - Plumbing, Overflow questions

[Kput]

Hello all! I've been searching through tons of Plywood tank build threads, as this site seems to be the best resource for them on the internet!

I am looking to have a 300~ gallon plywood built for a Reef tank. Thinking around 96x36x30, and after reading through all the threads I don't seem to be finding a lot of info on the plumbing aspect that helps me.
I will be running to a sump, and would like to mimic a traditional glass tank style plumbing as much as possible. I have not seen a plywood tank with a true corner overflow, however. Most I've come across are either drilled at the top with PVC for drains and returns, and I've seen a couple with overflow style boxes at the top, but no true info on the boxes.

Is it possible to drill the bottom of these tanks, and run a traditional corner overflow? I assume I'd either have to build the tank the appropriate size to fit a pre-fabbed acrylic corner overflow, and silicone it in, or go with a top overflow box?
I'd really like the plumbing to come from the bottom of the tank as it's easier to manage than digging around behind the tank..

Second questions is on bulkheads. Are people using just your typical sized bulkheads on the tanks like you would on a traditional glass tank?
I'm thinking of running 1" or 1 1/2" plumbing, ideally two drains, two returns, two overflows.

Pond Armor seems to be the best bet for coatings, and I imagine I will be fiberglassing the seams like I've seen on a lot of tanks. I have minor experience with fiberglass on car audio.. Are you guys using the same fiberglsas cloth? More than one layer?

Thanks for the help! Looking forward to replacing my 120 and moving up.

 

[jjohnwm]

The dimensions you quote are pretty close to 450 gallons, so...congrats! You just got a bigger tank!

I'll leave it to others to comment on techniques for applying fibreglass reinforcement. I have built a fair number of plywood tanks, although none larger than 96 x 36 x 24 inches, and have never used fibreglass. Never a problem. Just make sure your initial box construction is solid and square, use sufficient screws in combination with a good wood glue.

I use 2-inch bulkheads and piping for all drains. They're bigger than I ever need for the flow rates I have going, and having them all standardized makes my life easier. When ordering them, make sure the ones you get have a long enough threaded shank for use with a tank wall thickness of 3/4-inch plywood. Plan up front whether you want threads on both inside and outside, or unthreaded on both, or a combination.

Bottom-drilled tanks work okay, but nowadays I prefer holes drilled up at the top, at waterline. I put a bulkhead at that point, with a threaded union on the outside end. Fit a 90elbow to a short piece of pipe, attach that to the union, and then you can rotate the elbow up or down to adjust the exact water level; a useful feature. You can draw entirely from the surface with no further additions, or you can add a 90 and a vertical piece of pipe to the inside to draw from lower levels. If going that route, you should put a hole in the inside 90, which will allow some surface skimming and will also prevent siphoning down the main tank in case of a power outage.

 

[Kput]

The dimensions you quote are pretty close to 450 gallons, so...congrats! You just got a bigger tank!

I'll leave it to others to comment on techniques for applying fibreglass reinforcement. I have built a fair number of plywood tanks, although none larger than 96 x 36 x 24 inches, and have never used fibreglass. Never a problem. Just make sure your initial box construction is solid and square, use sufficient screws in combination with a good wood glue.

I use 2-inch bulkheads and piping for all drains. They're bigger than I ever need for the flow rates I have going, and having them all standardized makes my life easier. When ordering them, make sure the ones you get have a long enough threaded shank for use with a tank wall thickness of 3/4-inch plywood. Plan up front whether you want threads on both inside and outside, or unthreaded on both, or a combination.

Bottom-drilled tanks work okay, but nowadays I prefer holes drilled up at the top, at waterline. I put a bulkhead at that point, with a threaded union on the outside end. Fit a 90elbow to a short piece of pipe, attach that to the union, and then you can rotate the elbow up or down to adjust the exact water level; a useful feature. You can draw entirely from the surface with no further additions, or you can add a 90 and a vertical piece of pipe to the inside to draw from lower levels. If going that route, you should put a hole in the inside 90, which will allow some surface skimming and will also prevent siphoning down the main tank in case of a power outage.

This is how I've seen most tanks done, the only issue I have, however, is with the plumbing coming down the back of the tank I'm not sure I will be able to go 36" wide. I'd really like to be able to do bottom drilled with overflows so I can keep the tank tight against the wall, I'm just concerned it won't work, or will have issues. I have found corner overflows on ebay I can have customized to the tank size, and silicone in pretty easily..

Do you have any experience doing it this way?

 

[jjohnwm]

I'm too cheap to buy commercial stuff like that if I think I can build it myself.

I moved away from bottom drains after an incident in which a vertical standpipe screwed into a bottom bulkhead was struck or bent...not sure if by me or by a large fish...and ended up cracking at the threaded bottom end. Needed to quickly drain entire tank to fix and replace; major PITA.

If the corner overflows you mention consist of some kind of barrier that is siliconed in place across a corner and allow water to overflow at the top, you would largely negate the possibility of a problem like that one I had. Drawing water from lower levels could be arranged but would be more complicated. Personally, I've never tried anything like that. Looking forward to seeing your progress!

 

[Kput]

I'm too cheap to buy commercial stuff like that if I think I can build it myself.

I moved away from bottom drains after an incident in which a vertical standpipe screwed into a bottom bulkhead was struck or bent...not sure if by me or by a large fish...and ended up cracking at the threaded bottom end. Needed to quickly drain entire tank to fix and replace; major PITA.

If the corner overflows you mention consist of some kind of barrier that is siliconed in place across a corner and allow water to overflow at the top, you would largely negate the possibility of a problem like that one I had. Drawing water from lower levels could be arranged but would be more complicated. Personally, I've never tried anything like that. Looking forward to seeing your progress!

Yeah it would be like a traditional glass tank with overflows, acrylic barrier around the drain holes, siliconed in place. I'd run a traditional bulkhead, and Durso standpipes. I guess my only concern would be the integrity of the acrylic overflow and silicone, but if it's done properly I don't see a reason as to why it wouldn't work?

 

[jjohnwm]

I don't have any experience with acrylic, and not sure how well it adheres to silicone. Hopefully somebody else will pipe up who can answer this...?

 

[Kput]

I don't have any experience with acrylic, and not sure how well it adheres to silicone. Hopefully somebody else will pipe up who can answer this...?

Good point, I will have to research that as well.

Most overflows I've seen are siliconed to the glass, but maybe they're plastic and not acrylic?

While I've got you responding too, should I be using tempered or annealed glass? I'm seeing mixed answers..

 

[jjohnwm]

I've only ever used annealed glass, but mainly because I once did a bunch of drilled holes and had to avoid tempered.

If you're talking about the front viewing window of your tank, I don't think it matters which you use...but again, I haven't played with tempered so can't say for certain. I can guarantee that annealed glass of the appropriate thickness (and I admit that I always go up a thickness rather than using the absolute minimum off the charts) is absolutely adequate strengthwise, and if properly cleaned is easy to adhere to Pond Armor or other epoxies using silicone.

 

[Kput]

I guess now I'm running into a glass thickness problem. I'd previously been planning on 1/2 in glass, but going up to 30" height bumps the reccomendation to 16mm or 3/4. I cannot find anywhere locally that offers this thickness, I may have to rethink my dimensions.

 

[fishguy1978]

Acrylic does not like to bond to silicone or vise versa. Or is it other way around? Anyway, All-glass, Oceanic, Aqueon or what ever underwear name change has taken place uses plastic for their in-tank overflows.
Are you bracing the outside of the plywood with 2x4 or 2x6? If so are they perpendicular to the plywood (like building a wall)? If you do then you will have that air space behind the tank to run plumbing. Use schedule 80 bulkheads not the cheap kind that Aqueon includes in the megaflow kits. If installed correctly there is no reason to smear silicone all over them.