All the symptoms sound like the tank is too clean . No film algea for pods and snails to eat , no protiens for the skimmer to pull out . Cyanno and hair algea have a way of popping up and will probably go away as quick as they came . Maybe try running the skimmer less , feed a little more .

Phosphates are 0 mG/Lt. Though, I've read algae will expand to consume any extra phosphates so tests will usually read 0.

h2s - I'll remove the carbon and sniff for rotten egg smell in say 2 or 3 days? I don't vaccum though I have moved the occasional rock and once ran a credit card between the glass and sandbed to clear up some the brown algae spots. Is h2s poisoning quick or slow over weeks? Thanks 11Purewater and Ross.

Too clean - yeah it seems that way Toytech, though with the addition of the 2 cardinalfish I've significantly increased my feeding. Perhaps the filter floss is catching most of it. Previously I used the original mesh that came with the MP10 powerhead and it didn't get quite so dirty. Based on Ross' suggestion, I've removed the filter floss. Thanks, a "too clean" tank isn't something I'd even considered.

Silicone contamination - tank was built by Concept Aquatics which is a reputable tank builder in town. I have heard that one of the GE silicones isn't acceptable anymore so it is possible. I'll do more research. Thanks reefwars.

Thanks for the help everyone!

MH+T5 Odyssea lights are 1 year old. Would that be a likely cause?

I was under the assumption that cheato will feed on excess Phos/Nit. Also what type of bulbs and how high from the surface are they.

Your cheato however will die off from a lack of nutrients (lucky for you its easy to find someone giving away the stuff to replace)

If your bulbs are actually a year old I would begin with replacing those, also would cut back to a bi-weekly WC

H2S - Would only be a huge factor if you are stirring and disrupting the sand bed how long has your tank been setup for if it hasn't been a very long time I doubt you would have enough build up to cause a problem

What type of CUC do you have snail wise? Was it Turbo's that have died tanks really tend to show when one of those buggers die.

I also doubt that if your tank was built by any tank builder they would be not using a GE product especially if it was built recently. If you're still in doubt you could always call but chances are if your tank has been running for some time without problems from the start you're in the clear.

What are all your other water parameters?

Try to flood us with information the more you give, the more accurate response you'll likely to get.

And. Possible that its not cyano buy diatoms. Which need to run its coarse

Bulbs: 350w total of 10K MH and actinic T5 about 16" above surface
CUC: 1 hermit, 2x zombie snails, bristle worms, spaghetti worms and unfortunately flatworms.
Water params: ammonia 0, nitrite 0, nitrate 0, phosphates 0, salinity 35ppt, temp 24.3-24.7*C, aquavitro salinity mix

CUC is probably too small now. I'll add more.

Another vote for the "too clean" theory, thanks Hazratty. I'll sell the haddoni (too demanding) then experiment with running less clean. On one hand, I am putting far more food into the system than I was before this decline. On the other, before the decline I was doing water changes once a month or less with the minimal bioload. In any case, I think it is worth experimenting with.

Titus, it could be diatoms. A quick search sounds like diatoms are brown and cyano is red. I'd guess this algae is more red than brown. If diatoms, let them run its course. If cyano, then nutrient problem?

pm me for the haddoni , i could either buy or trade you some coral if you go that route:)

good luck

Curious if and when you fix the problem if you could give us updates. If your bulbs are older then a year I would change them out as well sort of a fresh start I guess that could also cause an algae/diatom bloom.

Oh and Good luck, I find sometimes fixing and researching and learning about the problem is almost as fun as watching it develop :)

I'm going to vote too clean as well. If you're deep sand bed is doing what it's supposed to, you should theoretically be at a really low nutrient level, and even though you've added fish, it doesn't sound like your bio-load is really all that high. And cyano is a tricky beast. It's presence does not necessarily mean you've got excess nutrients. It's a photosynthetic bacteria that is both an autotroph and a heterotroph and can survive in situations that lots of other things can't. I've always been really suspicious of the supposed causes of cyano, because if a lot of the 'common wisdom' about it was true, a simple course of chemi-clean shouldn't banish it forever from some people's tanks as it often seems to do. I have always thought of cyano more as an infection (it is a bacteria after all) than an algae.

Just my guess but lack of nutrient seem like your problem.

I would be worry about that thick sand as it may become anaerobic eventually and release some gaz in your tank.

There is not enough liverock to support good planktonic life. Try to feed zeovit amino acid and coral vite every other day. Pods eat phytoplankton so feeding the tank with live phyto will quickly bring bac the pods if any are still present. Of course stopping the skimmer for an hour while feeding phyto is required.

Your tank would be prettier with a bit more live rock. Now it looks empty and as if it's missing something, some substance. Try to find some nice shaped liverock (fully cured of course), or some nicely shaped dry base rock.

Also, I would never use carbon full time as you are removing some trace element from the water. There is no need for full time carbon treating. You would be best to use a skimmer only, no carbon.