I have a 180 gallon tank with 4 6-7 inch motoros. I have a sump, an emperor 400 filter and three power heads and a sterilizer. I checked my water quality tonight and amonnia was up a tad and the ph was wiped out. I was doing a water change one a week. i was doing two but dropped to one. If i go back to two a week would that be enough to keep those levels ok? I also feed these guys and gals twice a day. Frozen fish and krill. Thanks for any info.