There's also the totally non-automated, but hands-free system of which I am fond. All my tanks are drilled and equipped with bulkheads and valves. They are all connected by means of cut-to-length garden hoses to a manifold and pump that exhausts the waste water outside, at my choice either to my basement sump drain or to an outdoor tap which I use to water my flowers and veggies.
My water is from a well, never treated at all, but stored in a couple of large storage tanks in the crawlspace next to my basement. This lets it warm up to ambient basement room temperature on its own, for free. I can do about 350 gallons from these bins, which flows by gravity through more hoses into my aquaria. The bins are filled by still more hoses running from a cold water faucet installed specifically for this purpose. If I need more water at one time, I have an on-demand water heater that feeds directly to the tanks by means of...wait for it...more hoses!
I will point out that all hoses that deliver water to aquaria or holding bins are arranged such that when the water is turned off, they drain dry into those tanks. I never let water sit in a hose and then later enter an aquarium. I'm sure many aquarists who get turned on by banks of carefully assembled PVC pipes will scoff at this system, but it is easy to configure, just as easy to re-configure if needed to accommodate changes in tanks, inexpensive to build and it works perfectly. I can do an 80% water change amounting to about 550 gallons in all my tanks in a couple of pleasant, stress-free hours, which includes the time spent re-filling the storage vats.
All these hoses are permanently in place, clipped to walls, the backs of stands, the ceiling, etc. Between the hose system and the numerous strategically located valves, I can change as much or as little water as I want, in any combination of tanks, simply by opening/closing the appropriate valves and manually switching the exhaust water pump on and off. I never need to lift a bucket of water. I never leave the fishroom when water is running, either in or out...don't ask what brought me to that resolution. Despite my trade (industrial electrician)...or perhaps because of it!...I have a distrust of unnecessary automation. Sitting in a comfortable chair in my fishroom as water exits this tank and/or enters that tank, dog by my side, cold brew in hand, music playing...is my favourite relaxation.
Niki_up
, I'm curious. Why do you mention specifically re-filling with water a couple degrees cooler than tank water? I usually use water that is within a degree or so of the temperature of the tanks, and I wouldn't worry excessively if I had a 3-degree variance...but I wouldn't actually aim for that. What's the idea?