hello all! i am new to the forum, and have a quick question. i would like to create a 90 gallon discus tank featuring about 6-8 small discus fish. this will be an unplanted display tank, with a fluval fx 5, stocked with Chemi-Pure, and seachem matrix. in addition, i will use an Aqueon pro-flex 3, 20 gallon sump, as a refugium stocked with freshwater miracle mud, and alot of hornwort to attack nitrates.(and possibly a deep sandbed as well) i will also put more seachem matrix in the return chamber of the sump. return pump will be a magdrive 5, and estimated sump waterflow turnover rate approx 4 times per hour. now using this setup along with the fx5, how frequently, and how much water would i have to change to keep those discuss happy?