You understand about ammonia, and nitrates right? So now that your tank is cycled it creates nitrates at the end of the process, target levels are below 20ppm, in a heavily stocked tank nitrates are going to be higher. Your doing a 25% wc would be taking 100ppm down to 75ppm. Not that effective.. Atleast a 50% wc will cut the nitrates in half.. You should be testing your water too, making sure that your levels are not getting out of control..