My brother has a tank with guppies and last month 1 of them died with no visible cause as to why that happened. I tried telling him to have the water tested but he didn't get it tested. Today, his second guppy died. I went to my LFS yesterday which is about an hour away and that is where I have my water tested so my parents are not letting us go back today to have my brother's water tested. The remaining guppy has no visible symptoms of any disease. I thought guppies were social and need other guppies to live with but he doesn't want to get any more guppies. I was wondering if the remaining guppy would do alright in my 29 gallon tank with some mollies and cories. If he could live there is there any way I could make sure he doesn't have any diseases. I don't want my fish to get sick. I don't have room for a quarantine tank and I don't want his guppy to become stressed without any tank mates.