Zenia dying?

[Slyguy00]

I have not added any buffers, its purely from my water changes. I have been using Instant ocean sea salt. I do about 10-15% water changes once a week and clean filter once a week as well. I should add, i have a 50 gallon bowfront with a fluval 304 external ( and yes i know some people dont like them) but as long as I keep it clean it seems to do a very good job. It has carbon, phosphate remover, and fluval biomax medias, as well as the sponge filters.