The picture you posted is Gymnothorax tile, thhe Indian Mud Moray and it is very food-aggressive but shouldn't bother other robust fish. Just don't keep it w/ anything small enough to fit in it's mouth and also you must consider they can open their mouths VERY wide and swallow prey much bigger than you'd expect - and Shrimp was a favorite food of the one I just sold this weekend. It will also need to be graduated to brackish and eventually full saltwater as it grows. Maximum size is 2 feet, maybe selling it is a good idea.
Also, the 1 inch per gallon rule applies to the width and height of the fish as well - many people just assume it refers to length, so figure a 6" long fish might be 2" high and 1" wide, so you'd use the formula for a 9" fish rather than 6"
As far as rinsing filters, because chlorine kill Beneficial Bacteria on contact, it is better to rinse them in a bucket full of tank water and just use your fingers to rake across the surface. Other media can be added to the filters wherever there is empty space such as sponges, bio-balls, ceramic rings, lava rock etc
My advice is to set-up a larger tank and keep the bigger more aggressive fish in there, then use the 46g for smaller peaceful species
This is Gymnothorax polyuranadon, the TRUE Freshwater Snowflake Moray and the only TRUE Freshwater Moray that doesn't require brackish or saltwater
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