Diana K

Pond liners are pretty good that way. (UV)
Stock water tanks are even better, and are designed to not be sunk in the soil for support, but I would still sink these for the insulation. I doubt you could build them cheaper from concrete or concrete blocks. Maybe cheaper to dig the whole system into the ground and use flexible pond liner. Pre-formed ponds are not usually too deep. If you will be growing some of the larger plants you might want to look into stock watering tanks for some of the containers, to get the depth.

Tubs full of plants will have areas where the water is not moving so much, and mosquitoes will find these areas.

I like the rain barrel-auto top off idea. Pond liners can be plumbed together with bulkhead fittings and flex tubing. Even the fish can go from one tub to the other! Use a level to be sure all the ponds have water at the same height, or else build them together into a series of steps so water flows downhill from one to another, then pump it back uphill. Either method works. A pump can just as easily pump the water around in a circle with all the components level. If the power quits (say, armadillos eat the wiring) you would not risk all the water draining out of the system if all the ponds were the same elevation.

Lighting and sun and heat: depends on the plants you are growing. Crypts in general come from forest streams with dappled light all day, rarely or never full direct light. Other aquatic plants do get more direct light during at least part of the day. Time of year might make a difference, too. In the cooler months more direct sun will keep the water warmer.

Using a pump and in line heater might work, if you are just looking at a few degrees. It is very wasteful of electricity, though. The heat leaves the ponds very fast. I would still work with a greenhouse idea for the winter. Then, whatever heat the sun can provide through the greenhouse effect will be a great benefit.
You could also run a solar water heater. Gotta have some careful controls, though. Can't have it overheating.

Church

Wow, thank you very much, Diana! That was exactly the kind of info I was looking to get. I appreciate you pointing out the "over-the-long-haul" kind of advice that I wouldn't have thought about til it happened.

I think I've been convinced that I will need to make sure the water recirculates. I'm not going to great extents to filter the water or anything, so I'm going to make this basically just a continuous river, all at the same level to avoid the overflow situation. The plants will be providing me with all the biological filtration I'll need, and I'll work with that.

Would anyone have any suggestions on a substrate to use? Should I just go with whatever cheapest aquatic soil I can find at the hardware store?

davemonkey

Hi, Church!!

I think I'd go the El Natural route on this and use an organic potting soil mixed with some cheapie topsoil (or soil from your yard) , about a 70/30 mix (don't have to have that ratio, I'm just thinking CO2 from decomposing OM mixed with minerals in soil) and cap it with an inch of whatever you like (gravel, turface, aquasoil, sand).

This inspires me (except for the fact that I'm renting a house right now) to do something similar for an experiment station (to test "new" plants). You know, you could be completely natural with this. Light from the sun, filtration from plants, ferts from soil and fish waste (just like NPT), and if you need heat in winter, just throw up a small greenhouse structure over it (easy to do DIY on these) and BLAZAM, a large scale NPT.