DIY tank building

[thrlride]

Anthony,

I've been checking out your article in the Coral Magazine about the large pond and have a question for you...

I am making a topoff container that is 48" high, 25.5" wide and 7" deep. As you might be able to tell by the dimensions, it is going behind my tank. I was originally going to use the 2 part epoxy but I am really worried about that so after reading your article I thought that the pond liner might work.

What do you think? I used 3/4" oak plywood and used 2" screws every 2" or so to hold all pieces together. I don't have room to make any bracing like you did, would that be a problem with only 25 or so gallons?

Do you think it is necessary to put corner strips in there too?

Thanks for your help!

[Anthony Calfo]

When constructing aquariums from any of the common materials (glass, acrylic, wood)... a general rule of thumb is that is you do not go higher than 30" wide or high... you can go about at long as you want without undue cost (for thicker walls) and without extraordinary bracing (bracing is needed, for most of course... just nothing so involved as welding, four-sided captures, etc).

Even though this reservoir is 4' high... the ~2' length and 7" width are of little consequence.

Frankly... if you wanted to simply coat the inside of this wood trough with epoxy (non-toxic swimming pool paint, Tub and Tile paint, etc.... ie. Olympic brand, which I have used safely for fish and coral for years), then I see no trouble at all.

The liner is cheap and easy, but a bit awkward/cumbersome (very much so here with pleats and folds). Its the compromise we make (saving money) to get large pools at times.

Above all... without trying to pass the buck, here - there is a fabulous old book that few folks have or remember... but it details in one chapter the specific needs for building glass, plywood (regular and insulated) and fiberglass aquaria and pools!

Its called the Living Aquarium (old Crescent books pub.). Do look it up on Amazon or other used books sellers. Its a fabulous book

And please feel welcome to follow up here with more questions if/as needed.

And I wonder if you cannot just build this tank out of glass or acrylic my friend (easier)? Or do you prefer wood for durability behind the tank? Understood if so.

kindly, Anthony

[thrlride]

Thanks Anthony! I chose wood because an acrylic shop quoted me $375 just for the acrylic due to the height.

I've got a spouse that is concerned with the epoxy and frankly, she'd kill me if it ever decided to leak on her hardwood floors.

So the 48" height kills the idea then since there won't be any bracing other than the wall and tank itself?

Ryan

[Anthony Calfo]

not to worry, my friend... the 48" is fine in this case since the vessel is so small/narrow. You don;t need any bracing for a modest 25 gall tank like this.

Do look into used glass locally. 1/4" glass is cheap... and DAP 100% clear silicone is too ($4 or so). You could literally buy the materials to build this vessel out of glass for less than $30 in most parts of the country. Lots of local glass handlers replace retail/business windows and haul or even scrap 1/4" plate glass regularly. In fact... its worth so little money that it is more expensive to haul and recycle than the material is worth. Do look at the local glass shops again (or local hardware store)

[thrlride]

I would, but my wooden enclosure is already built.

You can see the pictures below:

[thrlride]

The verticle piece in the center was serving as a brace. If I did the liner then that would be removed. The step at the bottom, you can see in the last piece, goes around the floor molding in the house.

[Anthony Calfo]

I really am sure the liner is unecessary... but use it if it gives you peace of mind, my friend. Either way... coat the inside at least with tub and tile paint and caulk the seams. Failsafe

[thrlride]

I have the devoe 233h 2 part epoxy to put on it, just haven't opened it yet. So you think adding the epoxy and then silicon or caulk would be okay? To I need to coat the corners heavily? How many coats do you recommend?

[Anthony Calfo]

its really remarkable stuff... two coats is easily enough (and it dries incredibly hard like tub enamel!).

The key to plywood tanks is insuring they are built like a tank with no flex at the seams.

in this case... the vessel is so small, and screwed so well (every 2"), I do not expect that you will have any trouble.

Please do consider getting the above mentioned book first though. Its only around $10

well worth it with so much more fab info inside

[sfsuphysics]

That and pickup a DIY hardwood floor repair book at the library.. trust me in that you will drop water onto the floor, maybe even a minor overflow that will get under the tank stand and sit and chew on that floor

Btw Anthony is that book you mentioned is it written by Peter Hunnam? I'm thinking about a rather outrageous idea to make a reallly really long tank yet not have 1000gallons or some outrageous volume.

[Anthony Calfo]

yep... exactly so

first published in Sweden in 1981... later by Crescent books 1988/1989

[thrlride]

I didn't go easy on the screws, did I? LOL Lots of wood glue too!

I may coat it with the epoxy and see how it does, I can always fall back on the liner if that doesn't go good. I doubt they'd let me return the epoxy anyway.

If the spouse would allow me to run a 1/4" line to the garage, this could be avoided!

[RustySnail]

The pressure that the walls will be under is dependent on the height of the container. The area of the side walls will determine the force that the pressure exherts on the joints. Net volume 25g or 200g is not a consideration in the forces that the walls of the container will have on them (of course the larger the volume likely you will have larger wall area and depth).

From the picture thrlride shows; the box it 25.5" tall, 48" wide. The pressure exherted on the front and back wall is 1167 (lbf). This is a considerable amount of force, I would add a center brace at the top to minimize bulging of the panels and excessive bending at the corners. The brace in the center of the box is also adequate (if not better) for this purpose; but be sure and add more screws so the brace holds fast and the screws dont pull out. Be sure that this brace is fully sealed on all sides if you use it so that the wood does not soften at the screw joints.

[thrlride]

It's worse Rustysnail, this box is going to stand as you see it. 48" tall. The wood on top is also the lid I was going to screw down.

[thrlride]

I don't quite get how a 7" thick wall of water would exert the same amount of force as a 1/2" wall of water as a 30' wall of water given the same height. Can you delve in to that some?

[Anthony Calfo]

RustySnail... thank you for your input.

Just one question, mate: what are you smoking?

"considerable force"?!?!? This IS an exaggeration of... er, well... "considerable" magnitude.

The vessel is only 7" deep!

I've got Tupperware bowls that are wider, deeper, thinner and don't bow.

Seriously... your input is TRULY welcome. But please don't scare off this poor chap here with obsessive anal-retentive engineering for a mere 20 gall vessel. Yikes!

Practical is easily good enough here... we do not need specs on deflection, four-sided captures, etc.

Put another way... glass or acrylic aquariums of the same volume are mass produced in the thousands and have been so for decades. The 3/8 or 1/4" material (glass or acrylic again) have significantly less tolerance (higher deflection) compared to this reinforced, laminated Oak 3/4" plywood! And... they are made without center braces.

thrlride... do not worry, bro. But do be safe/conservative: again (as mentioned above), do wait to fill it until your book comes in the mail. Amazon has them used for just over $6. And... this reference has charts for tank size, vessel panes on scale(s) showing tolerances, etc.

Rustysnail... no offence This is just waaaaaay to anal for me, and honestly... too anal IMO for the greater good here by far

[RustySnail]

Oh I tought the open side was the top... Then double the number I just posted; it will be roughly 2300(lbf) net force on each wall. It sounds like lots of force; and it is, but with adequate bracing (maybe both the vertical center brace and bracing across the top) it should hold. Test fill it in your garage or on your back patio to see if the structure will remain watertight...

[thrlride]

Rest assured, it will be tested quite a while before it goes on the hardwood floor.

It will be behind the tank just as it is standing. 4 foot tall 25" wide and between the tank and wall which is slightly larger than 7".

[RustySnail]

thrlride-

It's really rather simple to determine... In fact it's a fundamental equation learned in the 1'st year of engineering school.

P = rho * g * h (rho is density of the liquid, g is acceleration to gravity, h is the height of the water column)

F = P * A ( Pressure from the equation above, Area (w*h) of the panel)

if you combine the two equations; the force equation becomes:

F = rho * g * h^2 * w

Force is dependent on the square of the height of the panel, not the width or the volume of the container.

Lets recalculate based on your dim's:

F = 1035 (kg/m^3) * 9.81 (kgm/s^2) * (1.21 (m))^2 * .6 (m) = 8859 (N) = 1990 (lbf)

Sorry; I doubled the first number when I should have recalculated it, but close enough for our purposes.

Anthony, sorry we disagree; just wanted to be helpful to the original poster...

[thrlride]

I wonder how much lbf a 3/4" piece of multiply oak plywood can handle...

[Anthony Calfo]

No worries... we all enjoy our hobby in unique/individual ways.

What one man sees as an unnecessary spend of time (excessive calculations, re-inventing wheels, etc.)... another man cherishes as an exercise in hard science, being thorough/accurate, etc.

But you/we must keep in mind the audience here: most aquarists do not have the means/mind, interest or desire to break out a micrometer, dust off an abacus.. and invite an eleven fingered friend over to engineer a plan to build a reservoir that holds less water than my 6mm thick plastic laundry tub (no braces there either BTW)

[thrlride]

You and waterkeeper crack me up with your way with words. LOL

Thanks both of you for all your help! I haven't decided if I'm going liner or epoxy yet but I am surely more educated now!

[Anthony Calfo]

my pleasure

[RustySnail]

Originally posted by thrlride
I wonder how much lbf a 3/4" piece of multiply oak plywood can handle...

Depends on the geometry; I could do the calc's but like Anthony stated, it's a question of how much time/effort in calculations someone would want to put into designing a wooden box that holds water. The only point I was trying to make is that there can be and is significant force on the walls of your water container (close to 1 ton of force in your case). A 3' tall rubbermaid container can hold the water; its not what they are designed to do, but they can hold it. Have I had em spring a leak? yep...

The added center brace will ensure that the walls dont deflect; its a robust design When in doubt, overbuild a bit and there will be no worries. Could 1/2" plywood do the same job? Probably. Its likely that 1/4" ply would hold the pressure, but it might be a bit hard to fasten together at the corners 3/4" with a brace in the center is plenty strong so long as everything seals up good.

I understand where you are coming from Anthony, it's your forum; and manly your advise/wisdom that we all come here to gain (which in general quite excellent). My post was in response to the general question that comes up about how to build a container like this (is it strong enough?). I was trying to illustrate that its totally dependent on the geometry of the container. If the box were a mere 1/2" thick, the same pressures/forces would exist on the front/back wall. I know it's hard to believe, but that's the honest truth. I figured that doing a quick hand calc for thrlride would be helpful in terms of his asking the reefkeeping community for advise (usually the answers are out there in the forums/community here on RC).

[Anthony Calfo]

no worries... it is indeed helpful information. And a good reminder for others building larger vessels not to underestimate the force of water.

A bit of an aside... it reminds me of when some folks move an aquarium with a little bit of water or wet sand/gravel in the bottom... then are surprised to discover a seam pulled and the tank leaks. Even just a couple gallons of water sloshing back and forth in a moving tank is a remarkable amount of force.

Anthony