proportinal adding of elements and whatnot to ideal SW levels. No issue of over or under adding. Also with your above scenario, your are missing cal & alk supplementation used by corals. unless you have just softies or fowlr
For the cost of biopellets, GFO, vitamins & trace element, and vodka dosing and all the extra's(testing, dosing, remebering to add, pumps, tumbling, etc)....probably just easier and cheaper to do the WC's...
I do however only change about 10% every 2 mos currently. Only skim and have near perfect params 0 nitrate, 420 cal, 8.6 Alk, .015 po4
I do have a doser that doses ALK & Cal, and I have a free channel so I decided to try & dose vinegar with it. (8ml/day) brought my po4 down from .025 to .015. I tried dosing about 20ml/day but was at 0 PO4 and didn't want it that low.
I did add some kent trace element for the heck of it to my cal mix to be added at the rate of 1.5ml/day. Don't know if it helps, but it cost me like $15/yr.
I use carbon ROX .08 at 1.5 cups swapped out every 3-4 weeks. NO GFO, NO Biopelets