Need to know when and how much. I have a 75gal DT with about 26gal in the sump. The tank is 4 weeks old and cycled. Would 5gal work to start with? Just put 14 crabs and 4 snails and 4 clowns in about 3 days ago. The numbers are good SG 1..024+/-, 0 ammonia, 8.2ish PH, 0 NI, 18-20NA. about a week ago my sand started in areas started to turn light brown. But now it’s brown and starting to creep across the sand from the left side to the right and on the LR on the left side just under the power head. Mostly on the left on the side with the power head. I know I need to add another something for more flow this weekend when I get paid. Could this be as simple as needing more flow in the tank?