+1 for Razorworm's comment. Otos are sensitive to water quality,if a tank is not fully cycled the ammonia, nitrites, and nitrates spikes could easily cause death. I don't add Otos to my tanks until I see diatoms or soft green flat algae types. If you are running out of food in you 10 gallon try Hikari Algae Wafers or blanched zuchini or cucumber.
We might need more info to help Is the 10 gal cycled? ? Are you moving the Otos to the main tank after quarantine or are you upgrading to a 20 gal? If the 10 gal is cycled just move the filter to the 20 gal along with the new filter (or put the media from the 10 gal's filter into the new filter if it fits) which will keep the 20 cycled for the Otos assuming it's a new uncycled tank.
I moved 3 oto's into my community tank after quarantine for 2 weeks, 1 of them died, I think due to ph differences. There was a 1 degree difference from tank to tank, and he was dead within 6 hours. I must agree oto's are very sensitive after my experience.
Last time i moved otos I drip acclimated them like I do for my shrimp. All 3 lived a good 4 months until sandy hit and we lost power. I definately recommend the drip method for otos since they are so sensitive
I have hard, PH 8.water. The first time I tried Otots, I dripped them for an hour, then put them in an empty qt tank. The tank had little algae and no visable diatoms. Just a few potted plants. I tried waffers, spinach and zucchini. They would pick at it but not eagerly eat. They all died. The next batch I dripped for 4 hours and put directly into an established heavily planted tank. They almost immediatly started cleaning the glass etc and chowed down on waffers etc. After a month, I moved their fat bodies to a community tank. Since the collection methods for these guys is so rough and they dont travel well, it is important to treat them with care, People say that Otos are sensitive and hard to keep. This is only true at first, Once brought back to health, they are very hardy. Again, consistant water paramaters are the key to success.
I bought a single oto, drip acclimated it for about an hour and put him in my moderately planted tank, 20g long.
After some research it sounded like he would be better off with a partner or two, so I got two more a few days later. Drip acclimated the same and added them to the tank. I was worried there wouldn't be enough algae in there for them to eat but they seem to do just fine. They aren't fat like I've seen some otos, but their bellies aren't sunken.
I cut up some cucumber, threw them in the freezer and put a couple half slices in the tank a couple times a week. I anchor them with a toothpick in the gravel. I've seen them all eating on the same cuc before, which is sweet. Turns out my red honey gourami really enjoys them as well. My otos never ate any of the algae wafers I put in there.
+1 for drip acclimation and adding them directly to a nicely established tank.