So my water doesn't foul up this is what i'm going to do for my 30gallon. Tommorow I'm gonna check to see if the fish are better (if the fungus is gone from the tail of that fish) if it is then i'm going to do a large water change approx 50% which should remove 50% of the medication. Then i'm going to put in a brand new activated carbon insert. I'm going to float a brand new filter sponge in my 10 gallon (which is stocked by lots of guppies who have eaten a lot today) right infront of the filter return so I can seed lots of bacteria overnight onto the sponge. After i'm sure i've removed all the medication from the the 30gallon tank i'm going to jump start the cycle in the tank with this sponge, i'm also going to toss in some hagen cycle (i have some laying around) just in case and I hope everything will turn out okay.