acro bleaching

[werp]

I had a purple monster acro bleach out on me over the weekend. This morning the tabletop acro next to it is starting to bleach. They have been in my tank for about 5 months. I have another purple monster that is about 1 month old and it and all other corals are fine. My nitrate, nitrite and ammonia are all 0. Salinity is 1.024. KH is 9, PH is 7.9, temperature is 78 degrees. What could be happening and what do I do? I do have the red flat worms if that matters.

[RobertG]

Werp, the ph reading you have given is this in the morning or night? It does sound to be low. between the light cycles the ph will drop. I would think cause the bleaching you are having.

I have had some ph issues lately & one coral has bleached a little.

[Instar]

If that pH was early AM, then no biggie unless it gets to 9 in the PM. Fuge lights can run at night to compensate for that.
The temperature has changed recently and that means you probably aren't running your a/c now. Also the evaporation rates have changed. If your tank temp swings because the house heat kicked on, that will also cause bleaching. Stained water from lack of changes or a skimmer running soft or some other sudden change will contribute. Old light bulbs will also cause health to decline and new bulbs are a sudden spectrum and intesity change that can cause bleaching. Check temp at different times of the day as well as pH. Check the temp and pH just before the halides go off and see what the highest and lowest points are every day. If your water changes and maint are regular, then that would not be it, but, if you neglected water changes for a while and then suddenly do a couple back to back, that can be a problem.

[matt]

I'd do a test for DOM (dissolved organic material) and you might consider water flow issues if the bleaching is limited to one area of your tank. I don't think the ph of 7.9 is anything to worry about, unless it's accompanied by low oxygen levels or high organics (those tend to go hand in hand)

78F is a little low for most acros; I'd bump it up to 80F and keep it there. I'd also make sure your salinity/specific gravity is accurate, meaning use a refractometer or lab grade hydrometer. You can also check for phosphate, but if you have high phosphate levels you probably also have a lot of algae. How about calcium level, what's that at? How are you repenishing calcium and carbonate?

Assuming that calcium, S.G. and water movement are all in good shape, I'd bet this might have something to do with high organics in the water. It's the sort of thing that can creep up on you over a period of time, then stony corals will start to bleach. Once it starts, you might have trouble containing it. Good luck!!

[werp]

I left my fan on last week after the lights went out. When I noticed that it was still going and turned it off the temperature was 74 degrees. I assume this may have been the problem. Thanks for helping me solve this mystery.