Test Results Are In

So I got my API freshwater master test kit in the mail do day and I have a few questions
For the 20 gallon tank with as of right now only 2 tiger barbs it reads PH 8.0, Ammonia .75ppm Nitrite 0ppm, and 10 ppm of Nitrate.
So I've got to ask how could there be 0ppm of nitrite with detectable levels of nitrate, and how do I lower the PH?
The 5.5 gallon tank with only a male betta fish in it right now reads; PH 7.8, Ammonia .25-.50ppm, Nitrite 0ppm, and Nitrate of 0-5ppm. Again what is the deal with the nitrate levels? Any thoughts on these freshwater test results would be great.

 

Overfeeding could account for the ammonia spike.
Having nitrate without nitrite is normal in established aquarium.

 

Check the nitrate reading on your tap water maybe?

 

Overfeeding could account for the ammonia spike.
Having nitrate without nitrite is normal in established aquarium.

Should I do a water change for either 20 gallon or 5.5.gallon or both, and if I do how much?

 

I'd make sure detritus is removed and check again after a day.

 

the 20 gallon needs about 70% wc.

the 5.5g about 30-50% wc.

please test your tap water.