You sound a bit down with this at the moment. Consider qualifying the advice feom people. Petco is not well known for keeping the best quairy plamts not livestock. Their job is to sell for profit and not foster the hobby.
You are merely keeping moss barely alive by putting them in a container filled with water. Moss, like all living things need several sources of nutrients. Consider going to home depot or walmart and picking up some liquid fertilizer from the garden section. That should have enough npk to boost some new green growth in that container. This advice comes from my own experience rebailitating some unwanted brown moss. The results were amazing. Try it and you will see. If u want a photo of the one i use, i can take a pic later