What kind of flys to use second week of august on the Leigh river?

Can someone help me figure out what I did wrong with otos? (Long details)?

• Sorry if this is long, I wanted to give adequate details, so someone can tell me where I went wrong and what I can do to prevent the future otos from dying, before I get anymore. ;) The tank is a 20 gallon, I cycled it and added a female Betta to it when it was finished cycling. She's been fine in the 20 gallon for the past year. So I bought 4 otos after making sure I had natural algae growth for them and after LOTS of reading about them. I know they're sensitive fish and kind of wanted the challenge of being successful with them. The tank is heavily decorated with long fake silk plants, river stones, driftwood (2), caves (6), an air stone, filter, heater, but also has a fairly open center of the tank. I put their bag in the tank for 3 hours, then released them. Oto 1 died after 3 days. I checked the body to see if there were any spots that I might have to treat the tank for or any swelling or gaunt-looking stomach. The stomach was slightly plump, but not near enough to be considered sickness. Nothing looked bizarre about it, and the otos had been sucking algae all day prior to his death. Oto 2 died after a week. Same exact scenario as above. No sign of starvation, illness or anything. Oto 3 and 4 had ich, I noticed as I was removing the dead oto. So I immediately upped the temperature of the tank. It was at 80 degrees, but I slowly raised it to 84, since that's safe for otos and Bettas. After 2 days, I tried ick guard. Oto 3 died within 24 hours of that. Now, fast forward to 4 weeks after oto 3 died. Oto 4 is still very much alive and ick-free with my Betta. They both seem content, but I do want to get buddies for my oto, since I know they're not loner fish. I have waited long enough to make sure the ick is definitely gone and the oto is definitely okay. It's been a month since the last oto, so I figured that should be long enough? Here are my water levels: PH: 7.4, and has been that way since day one with no fluctuation. Ammonia: 0 Nitrite:0 Nitrate: 15 Alkalinity: 15 Phosphate: 0 (Where I live, phosphate is fairly high in tap water, so I always check it and use prosphate remover.) I have an Aquaclear filter 20 gallon and a Marina 10 gallon filter. (Not for the purpose of trying to overstock, but to ensure if one breaks I have a back-up one that already has the beneficial bacteria in it. lol Both have almost no water current, so I know it's not stressful and both are always running.) I have an adjustable heater, I believe Fluval brand. Temperature stays at 80 degrees consistently, and I also have a thermometer, to check the temperature and make sure the heater is working. What did I do wrong? And how can I prevent it from happening again? I want to try to buy 2-3 for him, eventually working up to 6, but I don't want to murder anymore fish. By the way, I'm fairly new to aquarium fish, only having the Betta for a year. But I am very familiar with the chemistry of aquarium water, as I have multiple tanks with aquatic live rock gardens and live plant gardens. But plants and rocks are so much easier to keep alive than an otocinclus, it seems. lol

• Answer:

  You can buy more. Its sad to say but you can easily expect a 50% die off within the first few months. They don't handle being caught and shipped very well and tend to hold on long enough to make it into someones tank. You really didn't do anything wrong. However that one that did survive, if it lives through the next month, will be one of the hardiest least sensitive fish you own. Once they die off and a couple months have passed they turn into some of the most bullet proof fish ever. Seriously... My advice is to buy more oto's. When I purchase them I make sure that A - They have been in the store for at least 2 weeks B - They are fat and active C - I buy more than I want. If I want 6 oto's I'll normally buy around 10 - 12. Some will die off. So do not worry.. you did nothing wrong.