Aquarium Update

I don't know if I mentioned this before, but one of our fish died, and so far the other has seemingly been better off. We never saw either of them eat, but now that this fish is all alone he is eating more and more active. The quality of our water has improved as well, we recently filled the water back up in the tank because the water level was almost past the filter. The Ammonia and Nitrate tests ended up at zero. This has remained steady for the past few weeks. We haven't changed much about our water. We have just added some bacteria supplement.