bleaching due to light spectrum change?

[MrPuma]

I was wondering if anyone had any thoughts on this. The problem is I have had a green moonstone and a favia for about 6 months doing great. They were growing very well and in the same spot in the tank the entire time. Last week they started bleaching turning yellow and losing their zooanthellae. The water parameters are all within the usual limits. I have a maxima clam and an acropora that do not seem to be affected. I have a 36" X 18" X 20"deep tank with 2X175watt 10000K metal halide and 2X55watt PC actinics. My bulbs are 12 months old. I was wondering if the spectrum could have changed (ie.) emitting more uv or something to have caused the bleaching. my metal halides are usually on about 12 hours a day. nothing has changed over the past 6 months. I am planning on changing the bulbs here in a few days and I have purchased a lux meter to check the light readings where the corals are at with the old bulbs and then with the new ones. I would appreciate any help or ideas. Thanks.

 

[Anonymous]

It is possible that a lighting change could bleach a coral if all the bulbs are changed at once. But I would first look towards changes in temperature or salinity. Especially if they are swinging. The same goes for PH as well as any other parameters.

 

[Anonymous]

When bulbs age their spectrum changes in the other direction, i.e., less UV. My guess is that it is some other stressor.

What is your current temperature? Has it spiked recently?

 

[MrPuma]

I cant think of anything else that has changed except for the age of the lights. My parameters are as follows:

ph 8.2
salinity 1.024
calcium 475
alkalinity 3.5
temp. 79 real constant, have chiller
nitrites 0
nitrates 10
ammonia 0
iodine .03 hard to measure

 

[Anonymous]

Ok, I give up. Anyone else....?

 

[Anonymous]

Well,if it is your lighting it is not more UV light. It would be that the spectrum is weakening and is no longer producing the proper spectrum required by your corals.

If you plan on changing your lights make sure you only change one bulb per week,so as not to shock the corals more.

 

[Anonymous]

The other thing I forgot to mention is that you may have some sort of predator in your tank that is causing them to bleach. I would look by flashlight at night. Read up on pests and do a search here.