I am new to the salt side of the hobby, but if you are doing 5 gallon changes twice a week, that is 10 gallons a week, so that works out to about 8% (+/-). That in a 125 Gallon tank is low, from what I have read. Not to replace the experts here, but if possible, I think changing 5 Gallons a day (or every other day) may get it down faster and then try for 3 a week. that should get about a 12% change a week. JMHO, good luck.