Have you ever come across a creature in your tank that wasn't supposed to be there? It happened to me a couple weeks ago in my planted tank. I bought some plants and put them in and the next morning I saw something swimming around in there that looked like some kind of worm. After searching the internet I identified it as a leech! Sucked getting it out and now I don't want to put my hands in there.
Yeah... but my situation was different than yours.
About 8 years ago I had a different company servicing my tank than I do now. These bozos didn't sterilize their equipment properly. I know this because they caused a massive invasion in my tank. It was shocking.
So one night we come home late. I hadn’t turned on the lights on the tank all day and I needed to feed my fish. The house had been completely dark for hours. Normally, when I turn the tank lights on, there's still plenty of light in the house from the windows and house lights... but this night the house had been completely dark for hours.
When I kicked on the lights, I had to do like 6 or 7 double takes. I couldn't believe what I was seeing! There must have been 1000+ (no exaggeration) tiny snails crawling all over the glass. My saltwater tank is pretty much strictly for fish... I don't have live rock or live coral at all. If you have that kind of tank with live rock/corals... finding snails like this wouldn't be a real surprise because those things come living in the rock many times. But even in that situation... the extreme number of these snails would have been shocking. They were fucking all over everything. My service company had introduced these snails into my tank from one of the other tanks they serviced.
Apparently... these little fuckers bury themselves down in the sand until all light is gone. I never saw these things because they would never come out until the house got completely dark. You'd never know they were there if you looked at the tank during daylight or obviously when the lights were on. I had a FULL ON INVASION.
I called my bonehead aquarium service and told them about it. They didn't really believe me cause they had never seen the snails... and the numbers I was telling them about seemed impossible. I took a picture the next night and showed them. As soon as the lights go on, these little bastards high tail it into the sand and disappear. I fired those dipshits once they couldn't figure out how to eliminate the snails.
I accidentally solved my snail problem myself though. Not long after I fired the jackasses... I added a big Golden Puffer to my tank. This fish went ape shit in my tank almost immediately after I added him in. He could smell those snails down in the sand. He would go along the bottom of the tank sniffing... he'd locate one... blow a stream of water perfectly into the sand exposing the snail... then he'd eat the damned thing shell and all. In about 2 weeks... all the snails were eaten. He worked night and day sniffing those things out and completely eliminated them.