yeah once a week would be fine with just one of those fish in there but with all of them you really should be doing them every day or at least every other day (have your sister help with them since half of them are hers) oscars are really susceptible to getting HITH and the main cause of it is bad water conditions, and im sure your nitrates are through the roof in a weeks time. not to rag on you or anything, im just saying what you can do to help the fish be more comfortable in the meantime while your waiting on the larger tank. and a 125 still wont be big enough for all of them. maybe for the O, jag, salvini, pleco and one devil/midas (if it tolerates tankmates as it grows) but even then that will be a really stocked tank once they are grown and would need super filtration, and would be lucky for them to all get along. but yeah sounds like you guys dont have a good lfs, sounds like they will just sell you whatever in order to make a sale, i think pacus really shouldnt be kept in stock and should only be ordered on special request since they get SOOOOO massive and really need ponds and not tanks, as your sister has found out, they will make the space if they dont think they have enough and a 2ft long and several inch thick dinner plate of muscle can do some damage
