Thanks for the link - that is a little scary having only the check valve holding back disaster! I'd rather try a solenoid that is only open when it has power, maybe in combination with a check valve...
For the CL I don't have to wory about a siphon, but a plumbing leak would be bad...
I'm thinking about ways to encorporate the CL returns into the rockwork. I was planning on using some PVC "stands" to help support the rockwork anyway. So maybe I'll make them part of the plumbing. I'm going for some islands with lots of open space, that's the look I prefer. The tank is 72x24x24 and will be viweable from three sides.
I was thinking about the next pump up from the dart, but it is almost double in power consumption. That will also mean more noise and heat too I suppose. So I would like to make the dart work. Although I'll have a lot of elbows, I am going to try to have lots of outlets too and will try to use the 1.5" pipe wherever I can, which will help to reduce the backpressure from the plumbing...
I was thinking I'd have to have the nozzles at least 4" or so from the sand to avoid blowing it around too much, but really I'm not sure - I'll just have to try it I guess.