Did my corydoras eat my RCS's?

[Bear]

Story time:

I had a thriving heavily planted aquarium with 7 corys, 2 otos, 25 olive nerites, 8 amanos, and an indeterminate number of RCS's for a little over a year. I had to leave for a work engagement for about a month and had a friend (who knows nothing about aquariums) feed the tank a tiny pinch sinking wafers every three days. Friend told me the tank was starting to grow algae pretty bad, but I said, "don't worry about it." My octopus plants apparently took over the tank. I returned to a tank with horribly fouled water, ALL of my RCS's gone, all but one olive nerite dead and fouling the water, algae out of control with tons of that weird foamy algae that grows from too much protein. The Amanos all happy and healthy--nice and chonky--and all of the fish alive and healthy looking though hiding much more than usual. I'm still finding empty snail shells every once in a while after three weeks trying to recover my tank. My vals, java ferns, and amazon sword died from being covered in a film of algae. Crypts, octopus, dwarf sag, dwarf lily fine though disappointed in being neglected. The java moss died where I placed it and grew onto the log in the tank.

Tank parameters:
60 gal; "hot rodded" HOB; airstone; bubble bio MB filter
75°F
7.3pH
0ppm NH3
0ppm N02
10ppm N03
0ppm Cu
10 dGH
10 dKH

For an entire year the inverts in my tank have kept it great shape sometimes a little too much poop but nothing that was a problem. I had read that sometime neocardinias get some kind of black rot (from overcrowding, I think) that is very contagious amongst themselves and nearly 100% fatal if not dealt with. I took a sample of my water to the local aquarist shop to have them test to see if the water conditions were borked. They said the pH was a little high but nothing too bad. So I bought 30 more RCS's. Within a week, all gone, no corpses, no reds. I tested the water again with roughly the same result as above (I think the hardnesses varied slightly). I'm still battling the algae that grew on everything but the water remained clear and it is slowly getting back to being nice to look at. However, I'm very disheartened and on the verge of scooping up fish and amanos and re-doing the entire tank.

TL;DR Did my corys get starved while I was away and have a taste of shrimp and that's what they want to eat now? Why did all of my inverts except Amanos, and one olive nerite die, but the fish are fine?

 

Thanks for sticking through the story.

[eatyourpeas]

I have never heard of corys eating RCS. I have had massive die-offs of my RCS due to poor water quality conditions favoring parasites that ail RCS. It would explain why your fish were not affected. Have you looked at the dead shrimp for signs of fungus, or disease in their bodies?

This is a good guide to help identify problems:

https://aquariumbreeder.com/understanding-dwarf-shrimp-diseases-and-parasites/

[Bear]

Thank you for the link. It sounds like it might be Epibionts, Dinoflagellate, or Ellobiopsid Parasites as it impacted the snails too; but somehow my Amanos remain unscathed. looks like I go to medicating the tank to try to get rid of anything it might be.

[Beardedbillygoat1975]

I would agree with @eatyourpeas. This was a water quality related issue. If they were already dead the corys would scavenge. This sounds like the pinches of food were not so tiny. 

[JettsPapa]

On 12/3/2021 at 1:03 PM, Beardedbillygoat1975 said:

I would agree with @eatyourpeas. This was a water quality related issue. If they were already dead the corys would scavenge. This sounds like the pinches of food were not so tiny. 

That's kinda what I was thinking too.

[Bear]

Thanks, I was trying to understand why the new RCS's I added after I started cleaning up the algae would die off so quickly if all of the water parameters are in spec. It leads me to believe it's something other than just the water quality.

[Guppysnail]

On 12/3/2021 at 8:28 PM, Bear said:

Thanks, I was trying to understand why the new RCS's I added after I started cleaning up the algae would die off so quickly if all of the water parameters are in spec. It leads me to believe it's something other than just the water quality.

Did you treat with something to remove algae? It could be that or from large amounts of algae dying off all at once.  

[Bear]

On 12/4/2021 at 6:02 AM, Guppysnail said:

Did you treat with something to remove algae? It could be that or from large amounts of algae dying off all at once.  

No, I manually remove as much algae as I can, I save the liquid carbon for spot treatment of beard algae since that stuff won't even rub off in my fingers. (Many good octopus plants were sacri...unnecessarily pruned...for this cause *pours beer in the ground*) I usually let the back (algae) wall grow since it kept my snails and shrimp happy, but I'm pondering giving it a good scrubbing since the only shrimp that survived are the Amanos and they're big enough that they straight up hijack the food I feed the corys so there's little concern of them starving.

[eatyourpeas]

The culprit may still be living in the tank and attacking the new shrimp. I would wait a few weeks before adding RCS again. This would allow for several water changes and stabilizing the tank for them again.