Unexplained deaths

[ccc24]

Over the past week several fish have died in my main tank (I think we are up to 7). They have all been juvenile swordtails of the same spawn (born June 1st) except for one adult guppy. 
They all just show up dead one by one. No marks, no squabbling, no fungus, no sunken bellies, no growths, no wounds - nothing. The bodies look perfect. They are fine one minute and upside down when I get home from work. 
I haven’t been able to locate any stray current, the fish are all acting normal except the rainbow shark. It is acting listless and is hiding (very unlike him, he’s usually all over the tank). Appetite is all normal (except rainbow shark). Activity is normal. I have tested and retested the water, switched test kits and haven’t found anything off. I use this water in a 6g and 20g and those fish are fine.

pH 7.2

ammonia 0

nitrite 0

nitrate 20-30 (heavily planted tank and dosed to this level with easy green).

Any ideas on anything else I can troubleshoot?

[Colu]

Have you added any new fish or plants  to the tank in past couple of weeks that could have brought in parasites 

Edited August 27, 2022 by Colu

[SimmonsSnailsNScales]

@ccc24 I am just as stumped as you are on this one. However, if I were in this situation I would just go ahead and do the med trio on the entire tank in the hopes of snuffing out whatever is causing problems in the tank that is undetectable by a test kit. 

If you want to save money on meds, you can lower the water level in your tank as long as it is not super crowded with fish. If your filter cannot run at low water levels pop a sponge filter in there temporarily. Don't worry about the sponge being cycled because you will have to do frequent water changes during the medication process anyway. 

[ccc24]

On 8/26/2022 at 10:21 PM, Colu said:

Have you added any new fish or plants  to the tank in past couple of weeks that could have brought in parasites 

Technically, yes. I bought a batch of new plants and a few went in every tank around the house about 3 weeks ago. Fish, no. 

[quikv6]

Could the municipality have added any treatments to the water? (Extra chlorine, heavy metals, etc)

[ccc24]

Update - lost the rainbow shark and 3 more random fish. Right before it passed it developed the first outward sign of anything - a few red areas (beginning ulcers?). I had already been putting Maracyn for a few days with only maybe a touch of slowing to the deaths. So I switched strategies. Because of the speed of the deaths I assume either toxin (I’m doubting as there are 5 other various aquatic tanks in the house using the same water - including two African dwarf frogs that are not bothered) or bacteria. Maracyn wasn’t helping (gram positive) so I added Maracyn 2 for gram negative coverage. So far, this has helped. No deaths yesterday and no deaths so far today. I’m hoping with a full course of both, it will knock out whatever quick bacteria is wiping out the tank. 

[Colu]

If they developing redness or body ulcers it's more then likely a bacterial infection what I would do if you still experiencing problem's after a full course of maracyn and maracyn2 is do a course of kanaplex in food its a more broad spectrum antibiotic treatment that treats gram negative and some gram positive bacteria  feeding a small amount twice a day for 7 days 

Edited August 30, 2022 by Colu

[quikv6]

Quote

 

Maracyn and Maracyn 2 together may negatively impact beneficial bacteria.