I would not add rubble. 'cooking' floss for 18 hours is not likely to be too helpful. Usually a sponge filter with added bacteria would be my choice. Some of those bacteria, though, may be affected by the antibiotic. Thus, you may need (if its a problem - ammonia) - to do water changes more frequently.
yeah best I have then is a little rubber pot holder that's been damping the return pump which has been in there for forever.... but I doubt it's housing too much bacteria. If I do water changes do I just replenish the new water to the target day 1 concentration?
You want to replace the water with whatever concentrations that were in it before. i.e. the copper and kanaplex.
18 hours is not long enough for bacteria to colonize new substrate, it takes weeks/months. The reason why is that when you put new substrate into an existing tank, there is already a full population of nitrifiers living on the existing surfaces, so they don't as readily colonize newly added surfaces, and when they do, it is in low numbers. I prefer to keep a sponge filter running in a tank sump for this sort of use. Rubble rock that has been in the tank a long time also works, but can absorb copper medications.
I have not been. However I've done 50% water changes each day so far and I've been pretty careful about him eating everything that goes in the tank. I'll double check it tonight.
