What are these weird things in my tank?

BACKGROUND
I have a 20 gallon long with neocardina shrimp, two hillstream loaches, and one nerite snail (which disappeared). I left home for about 40 days, placed an automatic feeder on the tank and had my neighbor check on them. I came back to a crazy amount of black algae on all my plants which freaked me out, but I also left with 8 shrimp and came back to an army of about 50 so I figure the water parameters couldn't have gotten too bad. I have nasty city water, so I distill my water and add GH conditioner which has been working great for shrimp.

ISSUE
I recently noticed these three weird circle things in the picture (I circled them in yellow), I'm hoping somebody knows what they are? They feel hard on the outside and if 6 hours go by without checking the tank, I noticed they move positions by like 6 inches. I was hopeful they were loach eggs but the internet says loaches bury their eggs in the sand so now I'm paranoid it's something I don't want in the tank. Any advice would be appreciated, thank you!

It’s hard to see from those pictures but could they be snails?

Looks like Limpets.

Not loach eggs but I couldn't see the pics well. My hillstream loaches (sewellia) don't lay eggs like that, but not hard shelled.

Limpet's in my limited experience might be them. Nerites look like tiny snails even as eggs. They lay them everywhere.

MaloK said:

Looks like Limpets.

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I just looked up what a limpet was and it looks exactly like it. Thanks a ton!

fishorama said:

Not loach eggs but I couldn't see the pics well. My hillstream loaches (sewellia) don't lay eggs like that, but not hard shelled.

Limpet's in my limited experience might be them. Nerites look like tiny snails even as eggs. They lay them everywhere.

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You’re right, definitely a limpet. Thank you!