If it contains copper I wouldn't use it regardless of how low of a concentration. It could build up over time and negatively impact inverts and corals.my tank has unreadable no3 and po4, my mangrove is planted in the sand and I was thinking about putting in root tabs. Has anyone done this? Some fertilizers how copper and such, worried about effects on corals?
That said, I've found feeding frozen Mysis seems to help maintain phosphate. But, in my 40 breeder, I have to dose about 2.5 ml of nitrate daily to maintain my nitrate levels.