[Sk8r]

I use it with my 54g, and it does all I need: I have a reactor, but the stirrer is a mess. I gave up and just put a pound in my ro/di reservoir [32g], and cut a circle of eggcrate to hold the topoff pump on a fake bottom about halfway up the tub [to keep it above the slurry at the bottom. WOrks like a charm, cost, about 2.00 worth of eggcrate, compared to 300.00 worth of reactor and an 80.00 stirrer.

As for what it does chemically---it's pretty safe: if you ever goof and shoot a little slurry into your system, granted you're doing it from the sump, it's not going to be too bad. I wouldn't, understand, advise it, but it's a lot safer overdose than a lot of things. It will not raise calcium or alk, but in the presence of adequate magnesium, it will maintain the level you set by hand dosing. If mg falls, those readings will fall, so if you just test mg and keep ahead of the game and keep your kalk supply going, it never will drop.
It does have some grunge with it that won't dissolve, so ultimately you have to scrub the bucket out, every month or two. Simple trip to the household shower or backyard.

I don't know the fine points of dosing from both kinds of reactor, except that it is supposed to help support a calcium reactor, maybe also to help with ph.