Media Suggestions For Fluval U Series

The carbon pads in the u series, if I remember correctly, are white floss on one side and carbon on the other. Neither of these is particularly good for growing bacteria, though they will have some.
The best media to use would be some biomax from the box in the middle as that wouldn't have to be cut up. Just swap some biomax from the cycled filter with some from the uncycled filter. Since the 200 is rather overstocked due to the last owner, don't take too much. Even a small amount of cycled media will speed up a cycle. It's getting the bacteria started that's the slow bit.




Has your husband agreed to running both tanks ?

When you already have a cycled filter, there are two ways you can set up another tank.
The first is to use a bit of cycled media in the new filter and do a fishless cycle using ammonia. Although quicker than a fishless cycle without mature media, it still does take a couple of weeks or so.
The second way is to move media and fish at the same time. It is a bit hit and miss, but the aim is to move the amount of bacteria required by the fish you are moving. The problem is that different kinds of media will have differing amounts of bacteria on them. But in general terms, if you move a tenth of the fish you move a tenth of the media. You do need to keep an eye on the ammonia and nitrite levels of both tanks daily for several days after to be on the safe side. If you do see a reading for either, report back with the measurement and also the pH and temperature of the water. Ammonia is safe up to certain levels, but that level is dependent on the pH and temp. And nitrite is easily counteracted by salt, and there is a calculation to get the right amount.

Feed the fish less food for a few days before and after the move. Less food = less ammonia.

I'd do a 50% water change. The nitrite eaters are the most affected by doing things to the media, which is why you are seeing a trace of that and not ammonia. They should soon multiply enough to cope with the nitrite but keep your eye on the level just in case.

Strictly speaking, medication should be used within 12 months of opening the bottle even if it is still within the use by date. If the fungus doesn't clear up, run some carbon for 24 hours and try Waterlife's Myxazin or eSHa 2000. Fungus is usually a bacterial infection rather than a fungal one, though fungus infections are possible. The fungal one usually has white cottony strands coming off it. If it's just flat white/grey on the body, that's the bacterial one.
If you do water changes with med in the tank, if the med is dosed daily do the water change then add the med. If it is not dosed daily, add enough med to treat the amount of new water to replace the med you take out.