I have been reading your column for a long time and this is a plea for your help. I have been keeping marine fish since the 60's, before live rock, corals and skimmers. I decided to set up a display tank a while back and bought live rock in bulk and followed all the usual rules. I also installed a canister filter and have been gradually removing the bio-balls allowing the live rock to take complete control of all the biological filtering aspects. It is now running purely as a chemical filter with carbon and phosphate removing media. All has been going fine and the fishes added are a Mimic Tang, 2 clowns, Six Line Wrasse, Coral Beauty, Regal Tang and a goby. There are also hermit crabs wandering around and have a while back began to add corals. The tank readings seem to be ok, SG 1.026, pH 8.2, Temp 75, Ammonia, Nitrite, Nitrate, and Phosphate all zero. KH is 9 and Calcium 420. All fish and corals look happy and all seems well.
But I now notice some 'white' patches appearing on the live rock. (Hope the pictures are clear enough for you to be able to see what I mean.) I have read various books, searched the Internet, and talked to people in the fish shops about these white spots. Answers have ranged from bacteria die back to there's no such thing as bacteria dieback. What is this white stuff? If algae, why is it white. If bacteria, why is it happening? The other thing you may need to know is that the coralline algae is still growing and has recently covered the powerheads and continually requires removing from the front glass.
Sorry to trouble you with this saga and hope you can resolve it. I may be in a panic for no reason but in all my years of keeping marines, I have never noticed this before.
Thanks for your letter, and we are old timers at keeping marines - had my first marine aquarium in 1956!
Must say the photos are very blurry and cannot define what this substance is or may have been! Nevertheless, have seen white-like patches occasionally in aquariums on live rock as soft fungus-like growths (bacteria). They occurred on rock of different types/ages in those systems, but never to the extent as they appear in your photos. Those seen in past systems were caused by the die-off of some type of animal matter, possibly a sponge dying inside porous rock. And as to its cure, those rocks were either removed or the fungus siphoned out and ammonia levels monitored. But even that sort of happening is quite rare and seems not to fit what is somewhat visible in your photos.
Without more information I cannot make a judgment call as to what it is. As of now all I have to go on is it's a white-like patch and occurs on your live rock, and does not seem to be harming any creatures in the aquarium. I'll need more facts. - I wonder about the consistency of the white growths, e.g., is it soft to the touch? Is it hard to the touch? Is there anything under the growth/patch besides rock? Is the white stuff alive or dead? Was there anything on the rock prior to this white stuff coming about? Do any animals in the aquarium eat or pick on these patches?
Also, could you look this substance under a magnifying glass/microscope, as I've seen patches of algae turn white when there were not enough nutrients to keep them going. And it's like the survival of the fittest; some growths keep going while others of the same type of alga do not! Are these patch areas places where algae existed before?
Keep in mind bacteria growths would appear/feel spongy/soft, yet have some structure. Dead algae that turned white could be mushy, maybe containing some algae cell structure within. Check it out and let me know after you take a 'VERY' close look at it.
Fortunately, it does not seem to be harming anything in the aquarium.
Thanks for your prompt reply and took a piece of rock out of the tank and looked at it under a microscope. There is definitely nothing growing on or under the patches that are white. When I scraped the white stuff, its hard and crusty-like, not soft and mushy. Now that I think of it, I remember some of these areas had coralline algae at one time! But now its patchy white areas and no coralline in sight on these rocks! What killed the coralline, if this is the remains of coralline algae? Why would this happen in one place and not another in my aquarium? Could something be eating the live coralline and killing the remaining growth?
Now we are getting there!!! Now that I'm sure its not a mushy growth, and it was originally a growth of coralline algae, I'm willing to say this is simply 'dead' coralline algae, which 'will' turn white when the 'magnesium' level in the aquarium water falls below its needs to remain colorful, healthy and growing. Also, keep in mind the period of time this 'stuff' began turning white seems to correspond with when new corals were added (probably some stony corals), as both placed a draw on this element. In fact, coralline turning white is a signal that magnesium has fallen below what is needed to keep it flourishing.
You say the specific gravity is 1.026, therefore your magnesium should be at least 1300 mg/l, with 1350 a better number to attain and maintain. Check it out and let me know what it is, as I've seen this exact problem in not only some of my past aquariums, but many others when magnesium became too low to support good coralline growth.
Could be if magnesium is low, those other coralline growths, different species with different needs as to lighting and magnesium content will also begin to turn white sooner or later. Keep in mind coralline algae is about 40% magnesium. If you find magnesium low, there are many good magnesium additives on the market and recommend using them as directed until coralline appears to be flourishing once again. There's also I product I use to keep my coralline healthy and happy so to speak, and that is called Purple-Up by CaribSea.
I have now tested for magnesium as you suggested and got a figure of about 1200 mg/l, maybe less. From what you say I'm now fairly sure its just old coralline. I will begin to raise it and want to thank you for your patience. Now feel a lot better knowing this odd happening is resolved! Thanks much!