Rowaphos is non toxic so in that sense there is no issue adding large ammounts of ROWAphos to an aquarium. You will however find that because it is very effective at removing phosphate the speed that phosphae is removed can be an issue.

The main reasons for this are.

1.If PO4 is pulled down too quickly it can cause nutrient shock to certain corals.

2. When using too much Rowaphos you may notice a slight dip in Ph, any sudden change chemically is to be avoided and although this is temporary it is much better to avoid any dip in the first instance by using the suggested quantities on the tub.

3. Phosphate is still required in minor levels for various biological process in a saltwater aquarium and for plant growth in a freshwater aquarium. The use of excess amounts of ROWAphos may strip the phosphate down to zero and therefore disrupt metabolic processes.