[Iron Crab]

Over the weekend I did my tests and my nitrites were up to about .25ppm. It was time for a water change and I did a 10 gallon change and yesterday it was down to .05ppm and today it's back up to .1ppm. The tank has been up and running for 6 months now and everything looks great except my button polyps have closed up . I have about 240 lbs of LR. Ammonia at 0 and nitrates - if not zero close to it.
What's going on here? Is there a need to worry?
I'm using Salifert test kits.
Thanks, Bill

[reefhead]

no need to worry too much--just dont do any water cahnges for a bit to let the system try to take care of it.

you need to have some means of exporting the nutrients you add to the system (ie..chems,food...)

skimmer,macro algae,water changes are all forms of exporting nutrients. do you do all 3 of these?

sounds like a big tank, have you lost any fish lately?

[Rin]

Well, assuming that the test is valid, something has happened in your tank where the bacteria specific to coverting nitrites to nitrates are unable to keep up with the job.

Have you made any recent changes...added liverock or chemicals or livestock? Maybe something died and is rotting somewhere under the rocks. Bacteria that convert ammonia to nitrites grow more quickly. Maybe you had an ammonia problem just recently but missed the event between tests. Bacteria colonies also go through die offs as nutrients become scarce. You tank isn't very mature and may not have well-established colonies.

Another thing that I've noticed through my limited experience as a reefkeeper is that a lot of tanks experience a mini-crash at about 6 months. I don't know why this is. It's happened to every tank I've been around--only one of them was mine.