Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
New Substrate, Retain the Fish, Plants and Bacteria
A week or more before: Clean the filter and vacuum the substrate the best you can.
The day before:
Arrange all the equipment you will need, rinse the new substrate if needed, set up new water ahead of time if needed. I use garbage cans. Add dechlor, minerals, peat... whatever is needed to make the water ready for the fish. Circulating the water for a day or so dissolves whatever minerals you may add, or conditions it with peat moss, if this is what it needs. (I have filled tanks with 100% tap water, dechlor and added fish. Not a problem if the mineral level of the new water is what the fish are used to.) Make sure this water is the right temperature. (An aquarium heater can be suspended in a garbage can)
The day of...
1) Unplug, turn off equipment.
2) Siphon clean water from the tank into enough buckets. Put fish in the buckets, plants, and filter media into separate buckets. Cover the buckets with the fish. Fish jump. Separate buckets for separate species, or aggressive fish. Loaches separate. Stressed Loaches can produce excess slime coat that seems to kill other species in small volumes of water. Keep the beneficial bacteria alive in the filter or in a bucket, and the bacteria on the decorations by keeping these things damp. Large driftwood or rocks could go in a garbage bag to stay damp. The bacteria do not need to be covered in water. They do need high humidity and oxygen. You could keep some of the old water in more buckets. This is optional. There is not a significant bacteria population in the old water, but the mineral balance is what the fish are used to.
Skim the top layer of gravel and keep that damp. It has the highest population of bacteria. Remove the rest.
3) Set up tank, equipment, decor, new substrate, a few inches of water... then PLANT. Mist the plants a lot.
4) Fill the tank with mostly new water. You could use some reserved water, but it is not necessary if you have followed my step 1. Put a plate or plastic bag over the substrate and run the water in slowly so it seeps into the substrate. This will reduce cloudiness.
5) Turn the equipment on when the tank is full enough and be sure it is still working. Put the reserved gravel in mesh bags and hang them somewhere with good water flow. The bacteria in these bags will help for a while.
6) When it is time to add the fish, DO NOT use the water from their bucket(s). Stressed fish produce more ammonia and stress hormones. You do not want these in the new tank.
The rest of the day:
Lights out, do not feed the fish.
Next day and beyond:
Lights on, feed if the fish are acting normal, or don't feed.
Test the water for all the usual things. Be ready to do a water change if ammonia or nitrite are present.
Fertilizer the plants as needed, but you might go easy on this until the plants are established and growing again. Go slow with CO2 until you know how the new substrate reacts. If I remember, Floramax is one of those that removes KH and drops the pH. You can add carbonates to counteract that.
Remove one of the mesh bags with gravel. A month or so is plenty of time for the bacteria to colonize the new substrate and grow back if the population was compromised.
Comment about the nitrifying bacteria:
The current fish mass support just so many bacteria. It does not matter where the bacteria are living. If you add more acreage (new substrate) for the bacteria to colonize, they will, but it will take time. A lot of the bacteria stay alive in the substrate, especially that top layer. Some loss is to be expected. Usually a well planted tank does not have problems this way. The plants are part of the bio filter and will make up for small losses in the bacteria population. Just in case, here are a couple of ways to get more of the bacteria into the new tank.
A) Move most of the decor, that skimmed layer of substrate and do not clean the old filter right away.
B) Add Dr. Tim's One and Only or Tetra Safe Start to both tanks, after splitting fish and bacteria the best you can. Look for Nitrospira species of bacteria on the label. Do not waste money on anything else.
Approximate bacteria populations and where they grow:
A well cycled filter has about half, perhaps more of the total population, especially if you are using an Aquaclear or one of the canisters that have lots of sponges and other media that is not thrown away. Rinse and reuse! Conserve the bacteria!
The upper layer of gravel where there is the best water flow has about 1/3 of the bacteria. If you are running a UGF properly then there may be more bacteria deeper in the gravel. A UGF is not used with finer substrates.
Convoluted decor such as Texas Holey Rock, Lava rock, drift wood, and similar things with LOTS of square inches of surface may have as much as 1/4 of the bacteria, but usually not even this much. Smooth rocks, plastic plants, ceramic merpeople and other decor with little surface area have very little bacteria. Some; enough to jump start a fishless cycle. Not much when you are looking for bacteria to support a population of fish.
Live plants have both a good population of microorganisms, AND are bio filters themselves. If there are enough plants that you cannot see the back of the tank then there are enough plants that they can probably deal with the ammonia from a reasonable load of fish, even if you did not move any bacteria to the new set up.
Smooth glass or acrylic tank walls, heaters and other equipment does not offer much surface area for the bacteria, and are usually exposed to the light. The bacteria that we are trying to conserve do not grow so well in direct light.