Fuzzy rocks

[molly]

Have a 45 gallon reef tank that's been set up for ~2 years. Metal halides and blue actinic bulbs. 90lb live rock and 2" live sand. 2 doz snail/crabs. 2 urchins. Rabbit fish, lawnmower blenny & hippo tang to control "vegetation". 20% water change every 4 weeks. Chem always excellent. Temp 78 deg. Just lost a red tree coral and an elegance coral and have this strange fuzzy stuff (some places actually look like cob webs) growing on the rocks and even the pencil urchin. Any idea what it might be and how to get rid of it? Thanks!

[tresguey]

you wouldn't happen to have a pic would ya?

[hoodoo]

I would not do one big water change every 4 week. I would go with a 10% every week. That's not so much stress for the tank.

[Scuba]

It is probably from the corals the did not make it.

[molly]

Thanks everyone. Just trying to sort it all out:
1. Could the 20% monthly water change cause the problem or would smaller ones just be less stress on the animals?
2. Sorry, no pictures yet.
3. The "fuzz" appeared prior to the coral deaths.

[hoodoo]

well, when you do a waterchange you prob. do about 9-10 gallons. But with rock and sand and everything your tank probably has far less then 45 gallons of water. So it's already 30% (just a guess, maybe you calculated that in). It just is pretty stressful to change that water all at once. The new water is probably a lot different than the tank water.

On top of that you could have higher spikes in phosphates, nitrates or other bad things. They can add up for a whole month.
That might cause algae blooms and not having any pics of what you got there I would just think it is a kind of algae.

[Craig Manoukian]

Welcome molly, was just up in Portland!

What color are the "cob webs"?

[hoodoo]

and, how old are your bulbs?

[molly]

Thanks for all of the ideas. Tank capacity is 47 gallons + 3 in the sump. I change about 10 gallons / month. I make RO water with a Hi S membrane. SG @ 1.0235 (matches tank SG) and same temp, 78deg. The metal halides (2 @ 175w) are approximately 5 months old. The "fuzz" can't really be seen from a couple of feet away from the tank but if you get up close and look for it, it is on all of the live rock. Nothing on the tank surfaces, sand, powerheads etc. It is very fine and short (looks like peach fuzz) and somewhere between white and green... very light. The real problem is, it seems to be getting worse pretty quickly, I haven't seen any of the "cleaning crew" go after it & I don't want it to take over.

[hoodoo]

you should really take a pic of it.