Thanks for all your wonderful comments.....
The "drip system" consists of a Rainbird timer as used in outdoor sprinkler systems, (2) 3/4" solenoid valves which are controlled by the timer (one for hot and one for cold water), and 60 or so valves (mini w/o-ring) which are threaded into the side of a 3/4" schedule 40 PVC pipe which loops around the fishroom. It's almost the same as the loop for the air from the blower except it carries water, and the valves have to be suitable for use with water. About 2" after each mini valve outlet, and connected with standard aquarium tubing I located a drip emitter. They come in different metering rates. I have used 1gph, 2gph, and 3.5 gph emitters. Which rate I chose was determined by the tank size that each individual "dripper" is assigned to. The water is carried from the drip emitter to the tank using standard aquarium tubing.
For instance, using a 1gph emitter on a 20g tank for a timed period of 2 hours will deliver 2 gallons total to the tank. In short. a 10% water change. The slow rate keeps the tank temp stable. The temp of the water being fed to the tanks can be controlled by the ball valves that I have located after each solenoid. Water is added to the tanks at the opposite end of the tank from the overflow usually directly over or very near to the sponge filter. This allows for thorough mixing of the incoming water with the tank water. The tank level rises as the water is added until it reaches the level of the overflow drain, and then drains out to the basement sump pit.
Another benefit of this system is that it also eliminates the need to "top off" tanks.
The system can handle all the tanks at the same time.
Something worth mentioning here is that the tubing that delivers the water to the tank MUST terminate above the waterline in the tank, elsewise you can end up siphoning water from tank to tank when the solenoids de-energize. I accomplished this by heating until glowing, a metal rod slightly smaller than the tubing and melting a hole in the rear corner of the aquarium top frame by pressing the rod thru. Then I inserted the tubing down thru the hole leaving approx 1/4" of the tubing protruding thru into the tank. The tube can be held in place using silicone if needed if the fit isn't snug.
The water for this system comes from my tap water source. Luckily I have a well, so no chlorine/chloramine removal is needed. I am using unsoftened cold water and softened hot water at this time. All water that makes it to the tanks passes thru a 3 stage filtration system that finishes with a 2 micron filter. The water here is very hard, and has some iron in it. The 30 micron filter turns slightly orange from the iron after about 200-300 gallons. I figure I'll have to change it bi-weekly or so. A small price indeed for not having to do water changes on all these tanks.
As far as adjusting water chemistry, there are no provisions at this time to adjust anything besides temperature. I'll deal with that on a tank by tank basis if necessary. I've really never had to do much "adjusting" anyways.