Its really old atleast 5 years +
The question was for the other dude, Tangwich, but thanks for replying!
After reading your post and replies, one safe approach I can think of to make things better is to increase your bio filtration/bio media by either adding good quality cured live rock or cured bio media substrates eg. Sera Siporax to your sump and if needed, add an additional small powerhead to make sure the flow is ripping through the rocks and or bio media.
I noticed the filtration process doesn't work well unless there is enough flow ripping through the rocks and or media. Not that it doesn't work but I noticed a difference in coloration and growth; it's so much better to have moderate to high flow with additional bio in the sump rather than low flow with or without additional bio.
It's doesn't hurt if you increase the flow in the display a bit for the same reason but do take a close look to see if the sand is blowing in any direction, you want to avoid sand blowing as it can cause a negative change in the water. Even if its just a little bit, pay close attention because the little sand movement in the beginning can lead to a mount of sand shift the following day.
I had a similar problem I couldn't figure out for a long time a while back then my friend gave me a small basket of cured bio media. I got more live rocks from the LFS and as a result, I saw a big change. I had more problems I needed to figure out but the lack of bio was no longer one of them.
Water changes will help but only to a certain extent if your bio filtration is not up to par.