dying Otocinclus and Julii Cory

[Knew tooth is]

Here's a puzzle: I have three tanks, two 10 gallon and one 20 gallon. All three tanks have identical water parameters- pH, nitrate, ammonia (none), temperature, KH, GH, and pH. There is an otocinclus and also several Julii Corys, which have been breeding, in one ten gallon- Tank A. In another 10 gallon tank are a dwarf gourami, two gertrude blue eyed rainbow, and a molly- Tank B. In the 20 gallon tank are several mollies, blue gourami, panda cory, albino cory, otocinclus, dwarf rainbow, and pleco- Tank C. About 3-4 months ago, I placed some of the younger Julii Cory's from Tank A into Tank B.  The Julii Cory's in Tank B eventually died. Two days ago, I purchased four otocincluses and  placed two each in Tank B and Tank C. The otocincluses died in Tank B in 1-2 days. The otocinluses in Tank C are doing fine. I didn't notice any fish picking on another. The lighting is different, with fluorescent in Tank B and LED in Tanks A and C. Any ideas on what is causing the Julii Cory's and, more recently, the otocincluses to die? Another bit of information is that hair algae is growing on the amazon sword in Tank B. I've shortened the lighting duration and hoped that the added otocincluses would eat the hair algae. Thanks.

[SimmonsSnailsNScales]

This is puzzling. Assuming that you are absolutely sure that the water parameters are identical in each tank, I would guess that you have some sort of "sickness" in tank B that the fish in tank A simply are not immune to. I have not witnessed this personally, but I have heard mention of this happening in numerous aquarium coop videos. 

That being said if you do the med trio with all of your new fish in the first place my idea may be out the window. 

I am also fairly new into the hobby so if I am way off here, please let me know. 

[Cinnebuns]

Common death of otos is starvation. They exclusively eat algae. If the tank is clean of algae, they are starting. 

Another possibility is just bad stock. If they died shortly after you got them it's more likely to not be anything you did. 

Edited August 8, 2022 by Cinnebuns

[nabokovfan87]

If at all possible, please provide some photos and test results for each tank, including temps.

One of the bigger things to help on our side is to understand how things are setup.  If a tank has an airstone, hob vs. sponge filter, etc.

On 8/7/2022 at 11:10 AM, Knew tooth is said:

Tank A. In another 10 gallon tank are a dwarf gourami, two gertrude blue eyed rainbow, and a molly-

I would imagine tank temp is about 76+ or so.  Perfectly fine for Julii corys, it may stress Otos slightly.  They are a very small fish and in my care I try to keep them 70-74 with added oxygenation. Cooler water holds slightly more oxygen and it's a bit easier for them day to day.  They might do perfectly fine at warmer temps, but that's just a note.  I look online and everything says "70-80" for range, which makes me want to shoot for 74-75 as a target temp for that type of a listing.  Others can chime in and we'll see what everyone has their otos at.  Right now it's summer in so cal and so mine are at ~80 on a bad day.

On 8/7/2022 at 11:10 AM, Knew tooth is said:

Tank B. In the 20 gallon tank are several mollies, blue gourami, panda cory, albino cory, otocinclus, dwarf rainbow, and pleco

Probably the similar temp, pandas might be acclimated to warmer waters but generally prefer the cooler waters.  Part of it depends if they are hobbyist bred or east vs. west coast as well.  I believe the albino's are fine at the warmer range, but I'll edit/verify this one.  Otos again, might not like the 78 deg temps. 

On 8/7/2022 at 11:10 AM, Knew tooth is said:

Tank C. About 3-4 months ago, I placed some of the younger Julii Cory's from Tank A into Tank B.  The Julii Cory's in Tank B eventually died. Two days ago, I purchased four otocincluses and  placed two each in Tank B and Tank C. The otocincluses died in Tank B in 1-2 days. The otocinluses in Tank C are doing fine.

Temps on the Julii might not be compatible with the Otos, but it sounds like they might've just had some acclimation issues.  PLEASE watch this video and report back on how you fed them or acclimated them.  A big thing from this experience is to always try to keep them with wood.  Food with aufwuchs is also recommended.
 

On 8/7/2022 at 11:10 AM, Knew tooth is said:

I've shortened the lighting duration and hoped that the added otocincluses would eat the hair algae.

They might, but in my tanks they generally ignore all of the hair algae.  they prefer to graze on surfaces, new growth, and brush algae.  When I scrape the glass, the otos usually jump in and try to get the little bits that might be left.

[PotatoFish]

To build on the "bad stock" idea, did the otos from the store have a nice, round tummies when you bought them?