I have a 10 gallon originally one very small pleco and 5 cherry barbs. All of the cherry barbs died within a week of purchasing them so I decided to give it another chance by getting 5 fancy guppies. Those are all starting to die off now and within a few days but the pleco is still fine. I do water tests on a weekly basis and everything is coming up perfect, the water temp is in the mid 70's, and I use api stress coat and ph down for the water (just a bit because it can be a little high sometimes). I acclimate them by floating the bag for a half hour and they go in just fine but after 5 or 6 days maybe you start to see them on the bottom of the tank almost doing nothing. I actually work at the pet store where I purchased these from and we've never had issues like this so its definitely a problem at home. I'd be thankful for any advice.