It could work, yes. The only difficulty is in guaging what filter is best to move. The bacterial colony can't be judged by media size alone, the filters flow rate would come into play as this dtermine how much "food" passes through the media. I would move the larger of the 2 filters and the stock you suggest. Keep a close eye of water parameters, hopefully all will go well. The main area for concern tho is the smaller tank. You are going disturb the balance in there so this needs to be monitored very closely. Are you intending to keep the smaller tank going? If not just shift all your stock and filters, as you are only adding a snail and a molly to the load. It's quite safe, if you don't intend using the smaller filters, to simply put all the mature media from them into your new filters
yeah, my intention is to keep my smaller tank going but just lower the stock slightly. it is a lovely set up tank and the fish are really happy and healthy
i will try your first suggestion and put my fluval mini in the large tank and leave my marina i25 in the small tank. im pressuming my fluval mini is the better filter as it was the most expensive, i'd like to think this anyhow ha.
which fish and how many would you suggest to get the balance right.
ps its an apple snail ( roughly 2inch) and smallish platy currentl in the 125 lt
thanks for the help