Colony polyp turning fade

[kb20reefcentral]

My favourite colony polyps are losing their colour and beauty and turning to brown from red. Polyps are responding to light, however their beauty is going. Other polyps, mushrooms and zoanthids are doing fine. Any particular reason for it please?

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[hollister]

They still look healthy. For better help add tank specs in personal info.
Have you done anything differant latley?

[kb20reefcentral]

Not really. I dose Brightwell Replenish, Reef Code A&B, Iodine, sometimes micro bacter. I feed zooplant of TLF and weekly dose Seachem Fuel.

Tank spec:

Cal 500, pH 8, KH 9.6, NO3 50, SG 1.025, PO4 not detectable, magnesium not checked.

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