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Otos up and died in established heavily algal tank?


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  • pH = 7.2 (continuously monitored, by Seachem hang-in-tank, confirmed by API test kit)
  • Nitrates =between 20-40 ppm
  • Hardness = ?
  • Nitrite = 0 ppm
  • Ammonia = 0 ppm (continuously monitored, by Seachem hang-in-tank, confirmed by API test kit)
  • KH/Buffer =? (I put a bit of crushed coral in whenever the pH drops below 7.0)
  • Water Temperature  = 75°F

I've had 6 otos in a 55 gallon tank with 5 corys, 30 olive nerites, 100+ red cherry shrimp (only 10 adults rest are shrimplets in various stages of shrimplet-ness), and an estimated 10 Amano shrimp (I've only ever seen 6 at once, but I bought 10) living happily along for about 6 weeks.

Trying to reduce the overall algae in the tank I bumped up the lighting from 10/hrs to 12/hrs and a twice weekly full dose of Easy Green to two pumps per day every day so I could start tweaking the light and fertilizer until I found the right combination. In the past week the otos have seemingly vanished one by one but I thought nothing it since I never found a body and I read that they can expertly hide. The day before yesterday the plumpest looking oto of the bunch disappeared and today I found a mostly eaten corpse of an oto but no other corpses at the bottom of the tank underneath a lush crypt.

I'm super bummed that I lost all of my hyper glass-sucker puppies. Did I do something wrong? Did I miss something? Unusually bad luck?


Edited by Bear
had to delete picture it got corrupted copied from planted tank post
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I bought the otos and corys at the same time from the same shop. The shop said that they treat all of their newly arrived FW fish with antibiotics for a week before putting them out on the floor so I should be able to acclimate them to my tank immediately without quarantine. I took them at their word. I figured if there was something wrong i would've lost the otos well before they got nice and plump and sooner than 6 weeks for sure. Did spreading out the dosing of the fertilizer raise the nitrates in the water to such a point that they were toxic to the otos but not the corys or inverts?

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I don't think it was the nitrates as 20-40 seems reasonable. You have ample algae. They should not have starved, but perhaps they came in with parasites, and an atibiotic would not have helped. Your best bet is to assume that Otos are wild caught and may need a little extra care and medication. 

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40ppm nitrate won’t be great for but won’t kill healthy otos, but getting them healthy can be a bit of a trick. My experience is actually that a wormer rather than an antibiotic is a big help there. They’re often very starved coming in, and suck up all the waste from other fish that may have been in the same holding tank. As such, they’re prone to gut parasites.

Some people also have issues feeding them if they need more food than the tank directly provides.

Edited by AdamTill
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