Different pests need different pesticides. The key is to not allow any of the spray to get into the water (if possible) and to not over spray. Mosquitoes/fleas/ticks I treat the dog because anywhere they run in the yard/property they are susceptible to them. I don't know about ants, we don't have that problem up here.

I use a spray that you need an applicators license to get, so that won't help you much unless you have the license. I pay attention to what way the wind is blowing and don't spray where the wind can blow it into the pond. I use a permethrin based spray, and am very careful not to spray it near any flowering plants either close to the pond or away from the pond - it's deadly to bees.