Do you have pics for fish identification? Unfortunately, I can tell you already that your tank is overstocked, which would explain why it may not be able to keep up on ammonia. You should definately get a liquid test kit if you don't already have one. Test strips are ineffective because once you open the package and expose them to oxygen they start to break down. The meters that go into the water are also ineffective because they don't distinguish between treated ammonia and untreated.

Adding water is never a good idea unless you take water out. When water evaporates, it concentrates the metals and chemicals in the water. If you keep adding, you're just putting more chemical load into the tank. Taking water out before adding new water helps keep the dissolved chemicals at a managable level.