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
It's just I can never get a straight answer here, the moss in my tank get DIY CO2 mix, it also gets CO2 boost from ADI, and also plant grow, and another product from ADI that goes with the CO2 boost I wanna say its lush leaves or something like that can't think of the name right now an I'm out of the house but all those products are dosed the way according to directions on the bottles the only one I don't have an exact beat on is the CO2 mix but I'm gonna get a drop checker and better yet a real CO2 system. Thanks for the support yea that would be good if u can post or send the pic?