Two T5HO bulbs over a 55 gallon is very likely to be high light, assuming reasonable quality reflectors, and true HO ballasts in the lights. Your plants have been grown with high light, full menu of nutrients, and CO2. Those plants are adapted to the good availability of CO2, but in their new tanks at the store, there is no added CO2, so they have to adapt to that condition as best they can. At best they won't grow very well because they do need CO2 for the carbon to build new tissue at the high growth rate the light drives them to. The store needs to add a CO2 system, or limit themselves to plants that don't need high light and CO2, or sell their stock within a week of getting it.