You want the pH to be stable Dragon will adapt to your water pH and I recommended that you do not change the pH unless you need to:
Ammonia and nitrite 0ppm
Nitrate 5-10ppm and less than 30ppm
Higher nitrate could affect his immune response, growth, development, and can cause him to go into shock.
Dragon's water temperature is perfect! 5 gallon tank right? If so I'd say once a week clean his tank completely. Every day you could change 25 % of the water or you could even do every other day 50% of the water its totally up to you. Yes I THINK he is a delta tail not sure though
Hope I helped!