Strange discoloration event

My soft corals have started to whiten up a bit. One went through a period of hyposalinity but some mushrooms I added yesterday whitened up. I placed them under an overhang but they are still white albeit a bit more open. I doubt that this is a light related issue as bulbs were replaced months ago and some of these softies and LPS have been exposed to them for months. My nitrates are 0 as tested by a salifert test kit twice. Any ideas as to how to restore color?

 

Some soft corals don't do well with low nutrients. Also, stressors compound, so, with no stress, the light could be fine, but add in another stressor such as too much flow, high/low temp, toxins, metals, lack of nutrients etc... then light shock can kick in.

If your parameters are good, and the water isn't too clean, the flow is't too strong etc... you may want to look into toxins or metals. Are you running GAC and changing it regularly (i.e. less than 2 weeks or at least rinsing it under fresh water weekly)? If so, you may want to try a poly filter, metal accumulation can definitely cause bleaching.

 

I assume by GAC you mean carbon?
The problem with the metals thing is wouldn't the SPS bleach? I added an Acan and it starting to brown so I doubt its light. I will get TDS and phosphate tested as nutrients sounds most plausible.

 

Yup, Granular Activated Carbon GAC

No necessarily, a lot of people thinks our tanks are pretty contaminated with metals and yet SPS live and grow.

For example:
Down the Drain, Exports from Reef Aquaria by Ronald L. Shimek, Ph.D. - Reefkeeping.com

It is known that metals below, necessarily, toxic levels, can bind to certain fluorescent proteins and deactivate them.

Dana discusses some examples in this article for example:
Feature Article: How to Make Corals More Colorful Part 3 - New Information: Red Fluorescent Pigments: DsRed-type — Advanced Aquarist | Aquarist Magazine and Blog

You need nutrients to get browning, so, that would make me think
something along the lines of metals are more likely.

Often people will say browning is due to low light. However, browning is an increase in zooxanthellae. This can be in response to low light, but you still can't get an increase in algae (zoox) without nutrients. So, it would seem unlikely that it is due to light or nutrients in that case. Could be other stressors though.
There are a lot of things that could cause lightening, in order of likelyhood, to me, metals and toxins seem like the next logical step to rule out.

 

I will try toxins as parameters were:
Calcium: 380 something (hanna)
Nitrate: none (salifert)
Phosphate: barely any (hanna)

Any way I can test for metals?

 

Not much unfortunately besides a Poly-filter. Also, could run Cuprisorb, it won't "test" per say, but it will remove many metals. So, if you start to see an improvement, then metals would a possibility. A poly filter will also remove some, but not below trace levels, but that may be fine...

 

Also, BTW, do you have a PAR meter? I know you said that it is under an overhand and not getting much light, but perhaps there is more light bouncing off the glass or substrate than you think.