Phosphate testing inaccuracy some corals suffering

[Coral_Wife]

Over the past few weeks I've been been battling something causing poor health in some of my corals. Some have died, some are bleaching and some have bailout. I'll start from the beginning. Somehow we had a Salinity spike (regardless of having the ato). Got that level back down to 1.025. Gave it a few days and tested parameters, noticed high Nitrates regardless of dosing NoPox. KH was also high. I was using AFR daily, chose to stop until I get things leveled out. Bought the RODI and started doing water changes with that. Every other day 5g. This week.
Parameters a couple weeks ago were:
Phos: 0.12
Calc: 440
KH: 13
Nitrate: ^75. On Hanna and blood red API
Nitrite: 0
Ammonia: .25-.50
Parameters on 2/22:
Phos: 0.90
Calc: 460
KH: 11.8
Nitrate:^75 hanna and between 80-160 API
Ph: 7.4
Nitrite: 0
Amonia: 0
Today I wanted to check Phosphates again, I used the Hanna phosphate ulr before deciding on a nopox dose. Initially it read 0.00, so I said no way, checked again it read 0.22, then I was curious what a 3rd test would say and it read 0.11. So I dug out the API kit for a color range and got this (see pics). I do also have a bit of BHA on my Zoa tree. Any suggestions and help to steer me in the right direction is much appreciated.
Tank Info:
50g cube
Up and running 17 months
Refugium in order: filter sock, filter floss, bio cubes, skimmer, chaeto (added a week ago), chemi pure elite, Purigen, and Matrix (recently added).

 

[Gumbies R Us]

Bumping your post!

 

[eliaslikesfish]

Can you post current parameters? Sorry it’s taken so long to get a response.

 

[Wiskey]

I think you're on the right track with doing daily small water changes to get this in line. You don't want to change things too fast, but at the same time Nitrate and Phosphate of 75 and 0.9 is pretty high, and indicates excessive feeding, or a lack of filtration to me. I would be targeting maybe 20 nitrate, and 0.1 phosphate to be back at doing water changes weekly.

Once you get to that point then lets have a chat about your feeding routine, regular maintenance schedule, and equipment list to maintain it there and keep it stable.

Whiskey