This is a terrific setup! I'm glad I came across it, as I was going to do smth very similar as far as plumbing and arduino are concerned. Could you answer a few questions for me please?
Thanks and sure.
Do you have some trick that allows you to avoid over-the-top return and get this clean look?
I just have a very big return compartment in my sump that operates at just above the pump level so if there is power loss, water from the DT drains in the sump and there is no harm done.
How's the 700gph sound for you? Audible at all?
It is not silent, but it is not noisier than my MP40 either. As a matter of fact I'm glad there is a little trickle sound from there that masks the rumbling of the vortech.
What gph are you actually running after all head losses? What pump?
I haven't computed the GPH, but the pump (as stated in my first post) is an Eheim 1260 (602GPH rating) so I'm guessing I'm in the 350-400gph range, though I could be off by a lot. Either way I was going for about 10x my DT.
What relay boards are these? Where did you get them?
The boards are Futurlec opto-isolated 10A 4 relay boards from ... Futurlec

:
http://www.futurlec.com/Opto_Relay_4.shtml
For the price/convenience I don't think you can beat them. Add an American DJ power strip and you have 8 controlled strips for $60.
Did you by any chance get to networking that arduino box?
I have not had time to work on the Ethernet portion of the circuit yet. It is a proto board and there are some minor problems with the ETH circuit, but again, I haven't really looked at it. I've been working on coding the rest of the controller because I was on vacation for 2 weeks and wanted to make sure no disasters can happen while I was away.
Finally, the part that I didn't research yet at all are the probes... Did you pick any temperature or pH probes for your controller yet?
For temperature I'm using an LM35 - a linear temp to V IC that works pretty well. You have to, however, be a little creative to isolate it from the water as it is not waterproof. For PH, I use the BRS probes and they seem to work well.