I had them in a 125 tank for about 3 months. One of them I honestly thought was going to die. I had no other fish in the aqaurium with them. My Ph in that tank hung at about 7 and the ammonia level was at 0. The tank sat for three weeks with 20 Zebra Danios to cycle it. I removed them and added my Oscars mainly because so many people said the 55 was not good for 2. When the one Oscar became more lethargic I placed him back in the 55 gallon where after a week or so he got better. I added the second one and I'm not kidding the 2 of them quickly came together, like life was back to normal. As strange as it sounds that is why they are in there even if it sounds ridiculous.