Coralline algae bleaching?

[bd_scott]

Hello, I’ve recently run into an issue in which my coralline algae is bleaching and I’m hoping to better understand why it may be happening. I’ve recently upgraded my lighting to an aquatop marine (days ago) from the “freshwater” aquatop light I had for a few months. I know I’m not having an underlighting issue because I purchased a rock with coralline years ago and it’s never had issues, but started losing its color in spots today. My parameters are decent but i had a very scary alkalinity spike 3 weeks ago that i lowered through weekly water changes. a few days ago, another rock with coralline started bleaching and somewhat might be slowing down but i lost a significant amount. I test with api and hope to be upgrading to salifert soon

(30 gal tank)
phosphates <0.25 have always been here
nitrates 0
ammonia <0.25 definitely very close to 0
salinity 1.0245 (slight variations with evaporation)
ph is 8-8.2 on api and 7.89 on probe
calcium is 420
KH is 11 dkh

Are my low nitrates hurting the coralline? i used to have a very high amount but i’ve added a few coral frags, a turbo snail, and i have two hermits. and have slowly been increasing my water changes so i’m suspicious of the low low nitrates. But i also gave the tank way too much light for the last few weeks after leaving my new light on practically 24/7, so i’m wondering if that’s more likely the culprit. I’ve stopped this and am shooting for 8-9 hours a day now. Thank you in advance for insight

 

[Mattiejay6]

How old is your tank?

Coraline likes stability. With your low nutrients o would stop water changes for a bit and let them creep back up some.

 

[TigerReef]

Agree w/ @Mattiejay6 . Coraline likes stable parameters. The most common causes of bleaching are shifts in pH, temperature, and light.

 

[bd_scott]

The tank is a year old, but some sand, the purple rock, and the fish were all brought over from another year old tank.

I figured the swings were taking a tole. I already planned on skipping a water change this week to get nitrates up, and i’ll just feed a little extra and keep testing.

 

[TangerineSpeedo]

Alk spike yes... but it is most likely you switching lights. IMHO

 

[bd_scott]

Alk spike yes... but it is most likely you switching lights. IMHO

Since posting I started only having lights on for a handful of hours a day to really give the coralline a break. the purple rock has already bounced back, with the “white-ish” film flaking off pretty good. I was surprised. Thank you!