The LTA shouldn't have been able to catch and eat a healthy fish. Likely the fish were already dead before being blown into the nem. I'm sorry we can't come up with a clear answer for you, but it would be smart to pull all the fish for QT and start treatment assuming velvet. Here is a protocol that will treat many things at once and hopefully nail what you have going on.
This excerpt is found in this link and you can get more detailed info in the link
https://www.reef2reef.com/threads/velvet-amyloodinium-ocellatum.217570/
The short version:
- 5 minute freshwater dip
- Immediately afterwards, perform a chemical bath (in saltwater matching SG/temp the fish came from). You have two options:
- Acriflavine (preferred) - Do the bath for 75-90 minutes, but remove the fish immediately at the first sign of distress. Aerate heavily both before & during the bath, and temperature control the water. The following products contain acriflavine: Acriflavine-MS and Ruby Reef Rally. DO NOT mix acriflavine with any other chemicals.
- Formalin - Do the bath for 30-60 minutes max, but remove the fish immediately at the first sign of distress. Aerate heavily both before & during the bath, and temperature control the water. The following products contain formalin: Formalin-MS, Quick Cure, Aquarium Solutions Ich-X, Kordon Rid-Ich Plus. Use protection (rubber gloves, face mask, eye protection, etc.) whenever handling formalin as it is a known carcinogen! However, you can add Methylene Blue to the formalin bath (1 capful per 2-3 gallons of bath water.)
- After the bath, place the fish in a QT pre-dosed at 80mg/gal using Chloroquine phosphate. In theory, copper (exs. Cupramine, Coppersafe, Copper Power) should work just as well as CP. However, due to how fast velvet can reproduce you don’t have the luxury of slowly ramping up the copper level as is normally advised. Therefore, the fish needs to be placed in a QT with copper already at minimum therapeutic levels. This is the advantage CP has over copper in this particular situation.
- While in QT, use a wide spectrum antibiotic (exs. Seachem Kanaplex, Furan-2) for the first week to ward off any possible bacterial infections. Secondary bacterial infections are very common in fish with preexisting parasitic infestations such as velvet.
- Keep the fish in CP or copper (at therapeutic levels) for one month. However, you can transfer the fish into a non-medicated holding tank for observation after just two weeks (explained below). DO NOT lower the CP or copper level before transferring.
