I have been using AFR in my 135 Gallon system for 6 months now. Mostly LPS, some softies, and a few SPS. Works great! The one thing to watch for is on larger systems depending on your coral mix, you could use/need more Ca than the ratio in AFT. I have been two part dosing AFT and Carbo-Ca to see if I can get a decent balance. So far it is working out well. Admittedly I could do this cheaper. For me it's eliminating a risk factor, me. For the near future I will continue this path. As for the AFT brown/rusty color in the dosing container. I have noticed it. When I add more and stir it around, it goes back into solution. Same thing with the white precipitate in the Carbo-Ca. Hope that helps.