Coral bleaching cause?

[serbusfish]

First the facts you need:

Tank size: 75 Gallons
Lighting: Maxspect Razor 320W (25% Whites, 80% blues)
Equipment: Deltec MCE600 Skimmer, Phosphate Reactor
SG: 1.025
Cal: 420
Mag: 1380
KH: 8.5
Nitrate: 10
Phosphate: 0
Dosing: liquid calcium every couple of days, liquid KH booster every couple of days, 1 drop iodine every other day.

I have a large variety of soft and stony corals. A few of the stony corals are bleaching. A Birdsnest is slowly bleaching from the bottom on a few branches, a Forest Fire Montipora has a small amount of bleaching from the bottom, and one full branch of my Acropora Tenius has bleached.

The only change I have made to the tank involved removing one of my powerheads as it stopped working, this happened before Christmas and im stilling waiting on a replacement. At the moment the one remaining powerhead is doing a decent job circulating water around the tank but flow is reduced around my SPS compared to before.

I was also wondering if my nitrates my be the cause? They use to stay around 5 but testing today they are at 10. I have many corals doing great, Acans, Elegance, Bubble, Duncans, Monti Caps, Candy Cane, Acropora Florida, + others so im not sure what to make of the bleaching issue.

 

[DSMpunk]

Can you see polyp extension on the bleached parts?

 

[serbusfish]

Can you see polyp extension on the bleached parts?

The Birdsnest has some branches with polyp extensions and some that are smooth white. The Monti is smooth white, and the Acro has no polyp extensions.

 

[nmotz]

Difficult to know exactly...are the corals placed high in the tank or low? Sometimes if they are really close to the light they will get bleached ("sunburnt"). I would not think it was your nitrates. My nitrates are often higher than yours and I don't have bleached SPS. My acros are more brown, which is typical of a higher nutrient tank. But I have good polyp extension. I also have a monti cap with great coloration and two birdsnest corals that have decent color.

I did see some bleaching on the lower part of my orange monti digitata at one point and I think that was actually a result of the coral not getting the right spectrum of light. I had a 10,000K T8 fixture that wasn't cutting it. I switched to LEDs and the bleaching stopped, and I have better polyp extension now.

I wonder about the iodine? What is the purpose of that? I feel like iodine is probably not necessary, at least not that frequently. What are your thoughts on that?

 

[serbusfish]

Difficult to know exactly...are the corals placed high in the tank or low? Sometimes if they are really close to the light they will get bleached ("sunburnt"). I would not think it was your nitrates. My nitrates are often higher than yours and I don't have bleached SPS. My acros are more brown, which is typical of a higher nutrient tank. But I have good polyp extension. I also have a monti cap with great coloration and two birdsnest corals that have decent color.

I did see some bleaching on the lower part of my orange monti digitata at one point and I think that was actually a result of the coral not getting the right spectrum of light. I had a 10,000K T8 fixture that wasn't cutting it. I switched to LEDs and the bleaching stopped, and I have better polyp extension now.

I wonder about the iodine? What is the purpose of that? I feel like iodine is probably not necessary, at least not that frequently. What are your thoughts on that?

I have them around midway up. I dose iodine as my monti caps stopped growing and someone suggested lack of iodine can cause this, since I started dosing the whiteness has return to the edge of the coral which tells me it has started growing again.

 

[chilli_reef]

I would definitely dip them in the mean time.