Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Much the safest is to put the fish in a bucket while you swap out the sand. Here is how I would do this, and it is pretty fast, too.
1) Prepare new water as if you are doing at least a 50% water change.
2) Siphon the best water out of the tank into enough buckets to hold the fish, plants and filter media. (Filter media can stay in the filter for over an hour if it will get some oxygen) Put a lid over any buckets with fish, they jump. Wrap a thick towel around the fish buckets to maintain a stable temperature.
3) Skim the uppermost layer of substrate (1/4"-1/2") and set this aside. Siphon the dirty water and remaining sand out together, add more water (tap water w/o dechlor is fine) as needed to get all the sand out.
4) Rinse out the tank to get all the sand out. Drain the rest of the water
5) Put new damp substrate into the tank, add rocks, driftwood... create hills and valleys.
6) Plant, misting often.
7) Put a plate or plastic bag over the substrate and refill by running the water in slowly over the plate. This allows it to seep into the substrate, and minimizes clouding.
8) Put that reserved skimmed substrate into mesh bags (nylon stockings are good for sand) and hang these in the back of the tank. This is the part of the substrate that had the maximum amount of nitrifying bacteria, and you are keeping this bacteria in the new set up, for a while.
9) Net the fish out of their bucket(s). Do not use the water they were in. Fish under stress can produce stress hormones and excess ammonia. You can use the water from the plant buckets.
10) Start the equipment when the tank is full enough.
11) Leave the lights off the rest of the day. Feeding is optional. If the fish look OK, feed. If they are hiding too much, then skip feeding.
12) Next day: Lights on, feed. Test for ammonia, nitrite and nitrate. Be ready to do a water change if needed.
13) Over the next few weeks: Remove one nylon bag of old sand each week. This allows the bacteria colony to grow without any sudden large ammonia spikes that could harm the fish.
If you think the bacteria colony has been compromised you can add some extra bacteria from a bottle. Look for Nitrospiros species of bacteria. All other bacteria in a bottle products have the wrong species.