When are you testing? The ph is lowest after the lights go out I believe. I would recommend some power heads as well, it will only help your tank. It keeps the water circulated around your live rock and makes your biological filtration stronger in my opinion not to mention the benefit of more surface movement.
Frequent weekly water changes are the key to keeping low nitrates. also not overstocking and overfeeding. These are the key contributors of nitrates.
Did you do the large water change after you finished your cycle? if you did a 50% water change next week your trates would still be 20. And thats if they don't rise between now and then.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.