720gallon plywood build?

[Redtailedcat]

Well i guess its time to make a monster tank.

This will be my first D.I.Y tank never done one before. 1.5 years ago for any of you that saw my 1700 gallon in door pond build that was the closest ive done to a DIY tank.
So here it goes i plan on my tank being 120'' long 48'' wide 29'' tall =723.1 gallons
the veiwing window will be 20''x90''. Why so small you ask because i already have the glass.

Now that being said. im looking for some clues on what to seal it with. Theres so many things out there i could use instead of reading all of them. Im looking for what has work for fellow mfk'ers i know everyone will say something different but i wanna get a general idea of what works and what doesint.quick question for you guys and girl is it possible to use Flexseal to seal the tank is it fish safe will it last?

I have my filters figured out 2 300 gallon rubbermaids with bio balls,filter media,and two gaint sponges.with a laguna 4200 pump. witch should turn the tank over 5 times an hour.( i think this should be good enough correct me if im wrong)

Its going to be a slow build nothing over night. ill be building it one thing at a time.

the stand will be 2x6's and 12'' on center all the way around. and will be 120'' long 48'' wide 36'' tall.

Should i go with a stacked tank meaning stacking 2x4's to make the tank then put plywood on the inside?
or build 4 walls with 2x4's 12'' on center then put plywood in for the sides?
using bondo to fill the screw holes.sanding it use fiberglass for the seams and sand then use pond armor? is there other products like pond armor that arnt as costly?

 

[sashimimaster]

Stacked 2x4 is overkill IMO. You're just wasting material. With only 29" height you don't have that much water pressure. My tank is 30" high and I don't have any support except fiberglass layers. There is no bow or flexing whatsoever.

 

[Redtailedcat]

Stacked 2x4 is overkill IMO. You're just wasting material. With only 29" height you don't have that much water pressure. My tank is 30" high and I don't have any support except fiberglass layers. There is no bow or flexing whatsoever.

did you fiberglass the whole in side or just the seams?

 

[CJH]

So here it goes i plan on my tank being 120'' long 48'' wide 29'' tall =723.1 gallons
the veiwing window will be 20''x90''. Why so small you ask because i already have the glass.

Now that being said. im looking for some clues on what to seal it with. Theres so many things out there i could use instead of reading all of them. Im looking for what has work for fellow mfk'ers i know everyone will say something different but i wanna get a general idea of what works and what doesint.quick question for you guys and girl is it possible to use Flexseal to seal the tank is it fish safe will it last?

Should i go with a stacked tank meaning stacking 2x4's to make the tank then put plywood on the inside?
or build 4 walls with 2x4's 12'' on center then put plywood in for the sides?
using bondo to fill the screw holes.sanding it use fiberglass for the seams and sand then use pond armor? is there other products like pond armor that arnt as costly?

I'm also not a fan of the stacked method. Like the previous post said you can get by without any framing at that height but I don't think some framing is a bad idea. 12" on center is fine.

Any liquid rubber type product is going to be a more expensive choice since they need to have a very thick coating to waterproof plywood and because they are fairly low in solids, at least compared to an epoxy or polyester resin. But that doesn't make them a bad choice. Flexseal is going to be a very expensive choice due to cost and because it's even lower in solids to make it sprayable out of a rattle can.

As far as products like Pond Armor but not as expensive, it seems like the real world costs that people are paying aren't the same as the listed prices on their website. I can't think of an example off the top of my head but if you do some reading I think you'll find some examples.

But with that said, any 100% solids marine epoxy resin will be similar to Pond Armor. With an epoxy resin you can buy your own thickener and use it instead of Bondo for filling screw holes and to make fillets along the interior seams if you so desire.

What part of the world are you in? That might make a difference.

I have never used a liquid rubber type product to seal a tank but have used polyester, epoxy and epoxy paint. I personally wouldn't hesitate to use any of them again depending on availability. I also wouldn't hesitate to use some sort of liquid rubber. Liquid rubber makes glass attachment slightly different but that's not a reason to avoid it, IMO.

I would avoid using polyester or epoxy paint if I had to apply it in my home as they have bad fumes. Epoxy resin and liquid rubber only have a faint smell.

 

[Redtailedcat]

I'm also not a fan of the stacked method. Like the previous post said you can get by without any framing at that height but I don't think some framing is a bad idea. 12" on center is fine.

Any liquid rubber type product is going to be a more expensive choice since they need to have a very thick coating to waterproof plywood and because they are fairly low in solids, at least compared to an epoxy or polyester resin. But that doesn't make them a bad choice. Flexseal is going to be a very expensive choice due to cost and because it's even lower in solids to make it sprayable out of a rattle can.

As far as products like Pond Armor but not as expensive, it seems like the real world costs that people are paying aren't the same as the listed prices on their website. I can't think of an example off the top of my head but if you do some reading I think you'll find some examples.

But with that said, any 100% solids marine epoxy resin will be similar to Pond Armor. With an epoxy resin you can buy your own thickener and use it instead of Bondo for filling screw holes and to make fillets along the interior seams if you so desire.

What part of the world are you in? That might make a difference.

I have never used a liquid rubber type product to seal a tank but have used polyester, epoxy and epoxy paint. I personally wouldn't hesitate to use any of them again depending on availability. I also wouldn't hesitate to use some sort of liquid rubber. Liquid rubber makes glass attachment slightly different but that's not a reason to avoid it, IMO.

I would avoid using polyester or epoxy paint if I had to apply it in my home as they have bad fumes. Epoxy resin and liquid rubber only have a faint smell.

im in ontario canada. Im not trying to be cheap by any means or cut corners just trying to save on cost or the girlfriend will likly kill me. i would like to get away with out framing to have a cleaner looking tank. im sure 3/4'' grade plywood would be fine as long as i brace the top correct? i have noticed many of the epoxys and some paints i cant get here for some reason. another question is what screws to use? some say deck some say drywall does it really matter as long as you dont buy cheap screws i think ill be fine? now whats the difference with epoxy and epoxy paint? with any of the products i will have to fiberglass the corners and seams right? i dont mean to ask all those questions but i wanna do it right the first time.

by polyester do you mean the resin or cloth?

 

[CJH]

im in ontario canada. Im not trying to be cheap by any means or cut corners just trying to save on cost or the girlfriend will likly kill me. i would like to get away with out framing to have a cleaner looking tank. im sure 3/4'' grade plywood would be fine as long as i brace the top correct? i have noticed many of the epoxys and some paints i cant get here for some reason. another question is what screws to use? some say deck some say drywall does it really matter as long as you dont buy cheap screws i think ill be fine? now whats the difference with epoxy and epoxy paint? with any of the products i will have to fiberglass the corners and seams right? i dont mean to ask all those questions but i wanna do it right the first time.

by polyester do you mean the resin or cloth?

Canada is where the Zavlar line of liquid rubber products is sold. I know some people have had trouble with it but you could maybe find someone who can spray the catalyzed version.

I believe you can build a tank of your dimensions without framing. But I also believe you could use framing and still have the clean look if you sheet the outside with something. That would give you wall cavities for insulation as well. But all that adds cost.

If you fiberglass the seams you could technically get away with drywall screws but I really don't think this is a good idea. Use a stronger screw.

By polyester I mean polyester resin, which is sometimes called fiberglass resin. Fiberglass is the reinforcment, whether it be cloth, roving, or mat. For plywood tanks only use cloth instead of roving or mat.

Epoxy resin is 100% resin. Epoxy paint like Sweetwater is about 70% resin and 30% solvent. There are other types of epoxy paint but I would not use them in a plywood tank build.

At the height you want I would fiberglass all of the interior seams. Understand that this doesn't mean you need to use polyester to wet out the fiberglass. You can use epoxy resin on most fiberglass cloths and there are cloths made for liquid rubber sealers.

If it were me and I could only get polyester and liquid rubber without international shipping I'd use polyester to wet out all of the fiberglass, including the area around the window. I'd then attach the glass or acrylic and then apply liquid rubber up to the glass. I'd probably use a polyurethane caulk as well that the liquid rubber would adhere to.

Or I'd just use polyester and skip liquid rubber altogether. There is some debate here about whether polyester is fish safe or if it's 100% waterproof but these debates usually ignore all of the successful builds that area sealed with just polyester. But it's your peace of mind that matters.

 

[Redtailedcat]

Canada is where the Zavlar line of liquid rubber products is sold. I know some people have had trouble with it but you could maybe find someone who can spray the catalyzed version.

I believe you can build a tank of your dimensions without framing. But I also believe you could use framing and still have the clean look if you sheet the outside with something. That would give you wall cavities for insulation as well. But all that adds cost.

If you fiberglass the seams you could technically get away with drywall screws but I really don't think this is a good idea. Use a stronger screw.

By polyester I mean polyester resin, which is sometimes called fiberglass resin. Fiberglass is the reinforcment, whether it be cloth, roving, or mat. For plywood tanks only use cloth instead of roving or mat.

Epoxy resin is 100% resin. Epoxy paint like Sweetwater is about 70% resin and 30% solvent. There are other types of epoxy paint but I would not use them in a plywood tank build.

At the height you want I would fiberglass all of the interior seams. Understand that this doesn't mean you need to use polyester to wet out the fiberglass. You can use epoxy resin on most fiberglass cloths and there are cloths made for liquid rubber sealers.

If it were me and I could only get polyester and liquid rubber without international shipping I'd use polyester to wet out all of the fiberglass, including the area around the window. I'd then attach the glass or acrylic and then apply liquid rubber up to the glass. I'd probably use a polyurethane caulk as well that the liquid rubber would adhere to.

Or I'd just use polyester and skip liquid rubber altogether. There is some debate here about whether polyester is fish safe or if it's 100% waterproof but these debates usually ignore all of the successful builds that area sealed with just polyester. But it's your peace of mind that matters.

well i think i know what im going to do. use 3/4'' plywood pre drill all holes use a 2'' wood screw and glue all my joints once the tank is build i will line all the seams with fiberglass and use a fiberglass resin to make the fiberglass cloth stick sand it all. and finaly use epoxy resin to seal the wood so the tank is 100% water proof silicone the glass in place wait 7 days and fill. does that sound right? is that how you would do it CJH?

 

[sashimimaster]

I fiberglassed the entire surface including seams and corners. The epoxy/fiberglass serves two purposes. It waterproofs as well as strengthens. I coated over it with liquid rubber just as added insurance. But the structural rigidity is plenty with 3/4" sheet plywood. If you think about it look at a glass factory made tank. The one's that are 24" high only use 3/8" non tempered glass. If that thin little piece of glass can hold 24" of water how much do you really need for 6 more inches of water height? People who stack 2x4s are just wasting a lot of money and time. If you are really paranoid just do as CJH said build a frame. Just make sure to tie in top edges.

 

[CJH]

well i think i know what im going to do. use 3/4'' plywood pre drill all holes use a 2'' wood screw and glue all my joints once the tank is build i will line all the seams with fiberglass and use a fiberglass resin to make the fiberglass cloth stick sand it all. and finaly use epoxy resin to seal the wood so the tank is 100% water proof silicone the glass in place wait 7 days and fill. does that sound right? is that how you would do it CJH?

No. If I were going to use epoxy resin as the topcoat I'd also use it to wet out the fiberglass recinforcement. No reason to buy polyester resin if you're using epoxy anyways.

I'd also use epoxy with a bit of thickener instead of glue inside of the joints. I'd also dip the screws in it before driving them in (I'd have the whole thing dry fit and screwed together before doing this). Wood glued joints are very strong but the exposed, laminated edges of plywood do not form the best bond with regular wood glue. Epoxy works a better. It's overkill but if you already have the epoxy it does form a stronger mechanical bond with plywood edges.

 

[Redtailedcat]

I fiberglassed the entire surface including seams and corners. The epoxy/fiberglass serves two purposes. It waterproofs as well as strengthens. I coated over it with liquid rubber just as added insurance. But the structural rigidity is plenty with 3/4" sheet plywood. If you think about it look at a glass factory made tank. The one's that are 24" high only use 3/8" non tempered glass. If that thin little piece of glass can hold 24" of water how much do you really need for 6 more inches of water height? People who stack 2x4s are just wasting a lot of money and time. If you are really paranoid just do as CJH said build a frame. Just make sure to tie in top edges.

What epoxy did you use? Do I really need rubber too?


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