About 3 weeks ago I brought 4 otocinclus and put in my 12 gallon tank with 8 guppies and 2 gouramis . For first few days they all swam around fine. Then i could only see 3 otocinclus, now I can only find 2. I can't see any dead fish or bits of fish and my ammonia levels are fine. Are they generally amazing hiders or is there something I'm missing