Auto water changes set up for easy tank enjoyment. I did mine ala Sergio's thread with an Eheim 1250 pump, two RO type lines with electronic solenoid valves, and one float switch with relay to shut off the fill cycle for around $260 per tank - using digital timers. I have two timers per tank with on off sequences - first for drain cycle and then a longer, slower fill cycle. I used a tee out of the canister filter's return line to start the drain. It runs to the Eheim hobby pump and solenoid. They are plugged into the digital timer which kicks off the show. The drain run is about 21 feet to my utility sink's drain pipe using a $5 "drain saddle" sold by ROwatersystems.com. The drain cycle takes about 24 minutes to pull a bit over two inches off the top of my 90 gallon. I use 3/8 O.D. BLACK polyethelene tubing for all of the drain cycle (and most of the fill's) except by the fill's solenoid which requires 1/4" OD tubing. Also all the plumbing fittings and checkvalves are (mostly) John Guest brand available at either ROwatersystems.com or US Plastic.com.
After the drain cycle is complete, another digital timer opens a different solenoid valve on 3/8" polyethelene tubing pressured by my house's cold water tap. I have two in-line heaters running full out for an hour to keep the temp up. On five nights each week, I drain about 12% of the tank, then it fills back up on the second cycle.
I have a ball valve shut almost all the way on the fill tubing to extend the fill cycle's time. The float switch powers off the solenoid after the tank is filled up. A minute later the power to the float switch powers off, as a fail safe (I HOPE!). Both solenoids are the normally closed variety, meaning if they lose power, they close the valve.
Works like a charm.
I used some RO tubing fittings made by John Guest which plumb into my utility sink's drain and cold water line into the sink. So there is no plumbing involving copper and brazing etc. They are all plastic parts - available at ROwatersystems.com.The drain sequence's solenoid was around $75 (Asco 3/8 inch with 5/16 orifice from Grainger Inc.) and the other 1/4" solenoid was from Autotopoff.com ~ $35.00. I also purchased the float switch and relay from Autotopoff. The 3/8" and 1/4" OD polyethelene line was from US Plastic. 100' of 3/8" BLACK (no algae that way) polyethelene was around $12.00
You can read up on many of these components on Sergio's excellent thread. Both Scolley and Sergio use X10 modules to control their solenoids off a PC computer. Caveat with X10. One has to disable "local control", or you might get some very wet floors!
Three Tanks...Eheim 2128 & XP3-90G, Eheim 2128-65G, Eheim 2232-25G.... Tek 4x54 watt T5-90G, Aqualight 96watt PC 65G low tech, 65 watt Aqualight-25G.... Hydors-90G & 65G ... Flourite in 90, 65, & 25 Gallons, .... Auto Water Change/Auto dosing on 90 & 65 gallon..... AGA member......