sps tips dying and loosing color!

[RF17]

Hello everyone!

Im having a problem with my SPS. When i add them to the tank, after about 3-4 weeks the tips start dying, begins to loose flesh at tips, looses polyp extension, browns out then dies. i have a acropora Staghorn that is doing well but my Purple prostrata, Strawberry shortcake, lokani, monitor cap, are all loosing their tips and slowing browning out and dying. i have 3 LPS corals and they are doing great. I've checked for pests and found nothing.

here are my tanks specs:70 gallon reef (LPS, SPS, Zoas)

Filtration:
Bubblemagus 5.5 skimmer
Filter sock (change every 3-4 weeks)
Chemipure blue
Rowa phos in reactor

Chemistry:
CA: 440 - 400 (40 ppm change over 20 days)
ALK: 8.8
MAG: 1470 - 1425 (45 ppm change over 20 days)
PHOS: 0
Nitrate: 9-4.5 (4.5 ppm change over 20 days)
Salinity: 1.027
Temp: 78.2 - 79.8 (every day)

LIGHTING:
8 bulb dimmable T5 Fixture.
12pm - 7pm
Running whites at 45% ( 2 bulbs )
running blues at 100% ( 5 )
running purple at 100% ( 1 )

I ran whites at 75% previously but the tips of the sps were dying so i dropped the intensity to 45%. they started browning. I was giving them 480-510 par and now they are getting 360-380 par.

Flow:
1 MP40 ( 80% Reef Crest mode )
1 MP10 ( 80% constant mode )

please help! thanks y'all!

[lynchmob3000]

You may quit running rowaphos and carbon all the time, your po4 is low already

[lynchmob3000]

Run a 10 to 12 hour photo period with 5 to 6 hours of peak intensity.
Stop running carbon and rowaphos.
Once your p04 is up start using rowa again but maybe a little less than before so your not stripping too fast.
Make sure your water is really at 1.027 and bring it down either way.
Do a 25% wc and ride it out