help - shrimp won't survive in my 10gal - problem solving shrimp deaths
Hey everyone!
I have a very well established RCS colony in a 3.3 gal tank that breeds like crazy and never has any abnormal deaths (to my knowledge). I've had this colony for about a year or so. They get Hikari crab cuisine every other day to every 3 days. Plenty of berried females, large males, and saddled females. No other fish, just the shrimp. I only really top off the water with tap water treated with API tap water conditioner and some thrive shrimp specific fertilizer.
So I had a 10 gal tank cycling in SC over the spring semester, started in Dec of 2025. I bought the tank off FB marketplace with an airstone and a sponge filter and there was aquasoil from the previous owner. I put in driftwood, some plants, a lava rock, black gravel, and some of that bioactive sand I had from my first tank. I started to have an algae problem, so I thought...shrimp time! I drip acclimated 5 of my shrimp from the established colony for a couple hours and put them in there mid-summer (after testing for ammonia, nitrates, nitrites all 0). They all died in the span of like 2-3 weeks. some of them molted, some of them did not. I think the ones that molted were the ones that died, but I'm not sure. The females lasted the longest, but also died. I found planaria one day, figured they were killing the shrimp, and treated the tank for that with goat safeguard following the dosage rates found on a reddit page (staying on the safe side). No fish in the tank yet.
Then, I moved back to SD for school. The 3 gal made the move remarkably well (again) and the 10 gal survived well. I added some more plants (including floaters), another small mopani wood piece, and the algae continued to bloom (i think it was a light problem and i've gotten it under control). After letting it cycle for a bit again and adding a HOB filter as well, I continued to test parameters and decided to try 6-8 shrimp again. They were doing well but not making a dent on the algae, so I got a nerite snail and pygmy corys about 2 weeks after adding the shrimp. The shrimp lasted a solid 2 weeks after that and then started dying. I only saw half of the bodies when I fished them out most of the time (I saw a pygmy cory munching on a dead snail, so I think it's them and not planaria). Once or twice, I saw a full body and it seemed like they hadn't molted fully (white ring of death). They refused to eat the crab cuisine in the 10 gal (just ate algae), so I figured it was a calcium problem. Again, the females lasted the longest. The snail didn't want to eat and ended up sitting in the same spot for a week after the first couple days of moving around and then died. It's been about a week or so since the pygmy corys are doing amazing and the algae is under control. I haven't seen any planaria at all again.
I don't have a way to test gh/kh or TDS, but ammonia, nitrates, and nitrites have all been within normal limits every week before siphoning out algae/replacing water with conditioned/fertilized tap water (same as above). No ammonia spikes, no sudden mass die offs, no "gasping" behaviors, just one every other day this last time.
TL/DR: shrimp keep dying in my 10 gal, i want to put more in but don't want them to also die. also, can I use my 3.3gal shrimp tank as a quarantine tank for nano fish before putting them in the 10 gal?
Thank you for all the help and please let me know if I need to add any additional info!