See all my pony cories died and I loved them ! I do get fish die off after a while fir no apparent reason but suspect at some point I had a bit of old tank syndrome . Had upped my maintenance loads but nitrate out of tap is high at 40 . All floating plants snuff it due to filter flow ha ha even duckweed !! I wouldn’t be using literal mud from garden it would be proper aqua stuff but read some of them leech ammonia into the water and tamper with PH so quite wary of exactly how much and how quickly dies this happen as no info on the packs !! Why would I need to keep the old water ? If I kept old filter wet and added more bacteria can I not do a new cycle ? Maybe I need to do tests to see what mix works ? This water would be no mineral added to it plus tap do need to find the right mix of each so I know what to do on a water change