I had a previous betta in my 5.5 gallon who recently passed due to dropsy. I did a full water change and rinsed the gravel and filter media. Is this enough to prevent dropsy in another betta? The tank is heated with a preset aqueon 50 watt and filtered by an aqueon quietflow 10 with a prefilter sponge around the intake. Water tests came back with pH 7.5, ammonia 0 ppm, Nitrite 0 ppm, and nitrate at what looks to be 5 ppm. Is this good enough to introduce a new betta or do I need to replace every thing in the tank due to the last fish's death? I can't start the tank over because I have a single oto (he came from a bigger tank that crashed after 2 years) and two bumblebee nerites in the tank already.