Your ammonia should be 0.00, the nitrite should also be 0.00
if not, the tank isn't yet cycled.
At near 20ppm nitrate, your water is prime fertile soup for algae growth.
Under ten would be better. And no amount of filtration reduces nitrate, in fact the biological media produces nitrate if not cleaned enough.
The only realistic way to reduce nitrate is a lot of water changes, and cleaning gunk from out of the filter.
And although 10 hours of light may not be overkill, if you don't have plants, you might try having lights on only when you are home watching the fish, for many of my tanks my lights were on timers, coming on just before coming home from work, and on4 or 5 hours.