If you are not impatient, you can add a small number of GC and then wait for the control you want. If you do not overstock the GC, they will not be a problem as they actually eat less as they age. If my second pond ends up with too much submerged overgrowth when things settle down after 6 to 8 years, then I will add a couple GC to this pond. First, I need to let the desirable plants and aquatic life reach their balance.