What are these?

I'm rebuilding a 180G tank that's been offline for over 10 years (major tank disaster I couldn't afford to fix). I have had the sand and formerly-live rock sitting dry in trash barrels in the basement all that time. I cleaned off the junk from the sand and brushed off the rock, then put them in the tank. I've started a fishless cycle and things are going OK.

But I have something growing in the tank I didn't put there (intentionally). The sand is acquiring quite a lot of these little blobs. They're pinhead-sized or smaller, and under tank lighting they are pinker than they appear in these photos. They look almost like pink grains of sand. They're completely uniform with no differentiation. They're very soft and break up easily when poked with a probe. The smallest divisions on that ruler are 0.5mm. Any ideas what they are? They certainly did an impressive job surviving that long!


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Thanks very much, guys. I totally agree that this would be the perfect time to deal with flatworms, but I don't think these are flatworms (and I've seen a few!). They're approximately flatworm-colored, but they are completely undifferentiated. They're completely uniform in color throughout, and they're just round/oval blobs. I just took these photos: I'm sorry they're so bad, but when the lights are on my phone goes nuts and thinks everything is high-contrast blue. I'll try to get some better ones.

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There's a white patch in these photos where I scooped up sand for the photos I posted above. Nothing has moved on to it, and I see no signs of movement at all. Ammonia is fine but nitrites are still pretty high so I'm just getting things started. Whatever they are, they're doing fine at 78F, pH 7.7, 36ppt. I've only added some FritzZyme Turbo Start and ammonia. I added some Algae Barn coralline algae and phytoplankton, but it was too early to do so. I just didn't realize the products had such a short shelf life and my nitrites were staying high, so it was either pour them in or toss them. As you can see from the photos there's a bit of a darker biofilm just starting on top of the sand. Nothing noticeable on the rock yet.
Sorry - it's been a while, and the process for inserting photos confuses the heck out of me. I managed to get the first post flagged as spam, so you may be seeing this one out of context. Wait for that one to appear.


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RC Staff
Staff member
I'm sorry about the problems posting. I honestly have no idea what you have there. I wish I could be helpful ?
Thanks, John. Since I'm not going to do anything until the nitrites come down, I'll just watch and wait. If they're growing, it's not very fast. And if they're not getting worse I'll probably just start slowly with a few detritivores and see if something starts to eat them.