Kristin: I'm pretty new to this also so I can't give you all the details...there must be a FAQ here someplace that can do that. It does sound like you are the right track though. I have thought of concrete for a fishpond also, and like you I was worried something in the cement that might be harmful to fish, like lime maybe? And then there is the possibility of a crack down the road that would leak water. I ended up using an old watering trough....but since I then worried about rust, I lined it with clear plastic, they do it with swimming pools, right? You could do that with cement too I guess.

I keep "feeder" guppies in the bottom half of my fountain. They are breeding out of control, but maybe these suckers can live anywhere? You can find the details of how the bottom was made on my old website...sorry it's gone a little crazy since they moved everything to a new server.

Here is a link that might be useful: Fountain index

Well, they pour concrete ponds, so there must be some way of leaching out the excess lime and making it habitable to fish. I just don't know what that is.

Kristin

Cure it I would think is pretty much it... more or less same as any other project.. jsut watch it, and check into test kits in regards to how water effects it. Don't know about reinforcement at that size... I think most embedded metal recomonds an inch thick coat over the metal.

I've been kicking around (for a long time) to attempt to build approx a 200 gal, outdoor aquarium for a saltwater application.... :-) I'm no where even near ready to start yet

kristin,
I am planning to try something similar and will probably use a liner like is used to line ponds and water features. No need to make the container water-tight that way and no concerns about toxicity as long as the liner is approved for fish.
Hope this helps.
Jeff

It can be done, people have done it. The professionals line the concrete with either a completely different material (ie. the concrete is just structural supporting something else that is actually the aquarium) or use a concrete sealer such as Thoroseal. Amateurs have done it with extensive leaching in vinegar baths, but I really suspect you will still get pH problems and will probably fail with sensitive fish. Might work better for saltwater than fresh.

I don't think a straight concrete container 1inch thick will be strong enough. I recently built a 3.6mx0.9m by 1.2m deep fishtank out of structural plywood and hardwood, and did all the design calculations. It is possible to work out the strength required, although it's a little difficult for concrete, as concrete is very brittle and has a low tensile strength.

The average force on the wall will be about 230kg/m with more force near the bottom and less near the top (however, tanks are usually cross braced at the bottom and open on the top). Think about the tank as a 24" slab with a 1000lb weight in the middle and think how strong it would have to be to hold without cracking. A circular tank will be stronger, and putting reinforcing wire, rod or fibre will make it more practical. Chicken wire wouldn't do a thing, but fencing wire, hardware mesh or fibreglass mesh would probably work.

You should put the reinforcing on the outside of the tank.

It's going to weigh a lot!

As an alternative idea, you could use a foam core of 2inch polystyrene boards with (3?) cement-acrylic and fibreglass layers on the outside and inside with through links made from light wire. It would weigh a lot less and it's really only the surface that you need to be concrete.

We are looking to make a small waterfall for our small pool and wanted to know if there is any concrete or mortar that would be safe for the fish. We have the rocks, but just need to know what to use to hold them together.
Thanx

I don't think there is any specific product that is better than others. I think the key is not to use it while it is fresh. I would wait at leat a month and either submerge it in water with water changes for a curing time. Or keep spraying it off and you should be okay. That is on my next list of to dos.I have decided to make it in three seperate pieces, for easier handling.I may try doing some sandcasting for the shapes, or use styrafoam and a wire armiture to build up the shape. I have been trying to get some silica fume or metakaolin to make a strong light weight alternative . Rick has been having good success with his mixes being light weight and strong.Maybe some one else has made one and they will post some pics.
Cindy