Ca reactor output directly into tank?

[Delphinus]

I'd be a little leery about trying it without a pH meter. I'd say just pick up the meter at some point and then give it a go. If you already have the reactor and other related equipment, that is, and it's just sitting around not getting any use.

On the other hand, a 20g with SPS-load could easily be maintained affordably with two part dosing. A pain to dose 2-part, you say? I saw a brilliant automated 2-part dosing mechanism that involved having the 2 parts premixed in something like a pop bottle or a milk jug, and two air pumps on timers that basically pumped air into the jugs, pressuring them and thus pushing the additive into the tank via air line tubing. The timers were on a 12-hour offset from one another so the one part would dose in the morning, the other in the evening.

The only thing is that the plan did involve some tricky cleverness to regulate the amount dosed, and off the top of my head I don't remember what that was.