I am trying to reduce the murkiness of my tank by adding charcoal, in addition to the packs in the filter. The store recommended activated carbon pellets and cheese cloth, or a filter bag. Can I put this directly in the tank, or will that be detrimental to the fish? We have 1 Koi, 4 goldfish and 2 plecos in a 55 gallon tank and are planning to upgrade to a bigger tank in the next couple of months. Thanks!