Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Algae grows where there is light, so it is not likely deep in the substrate.
Here is one way that might work, and I am sure you can work out variations.
Before you start prepare enough new water to do at least a 100% water change, perhaps more. Keep this water warm (tank temperature).
1) Drain the best water from the tank into as many buckets as needed for the fish. Cover the buckets. Fish jump. Fish are less stressed in the dark.
2) Plants, decor and equipment in other buckets.
...2a) Plants: Treat the plants in the buckets for algae. You can dose Excel OR hydrogen peroxide OR bleach OR algaecide in the buckets. Do not mix. Research the dose and timing. Have the neutralizer ready. Excel or H2O2: A bucket of fresh water. Bleach: A bucket with double dose of declor. Other materials may use other neutralizers.
...2b) Equipment, rocks, ceramic merpeople can usually be treated with bleach, then rinsed in a bucket with double dose of dechlor.
...2c) Things like driftwood that might absorb the bleach are probably better treated with hydrogen peroxide or excel. Traces of these that get back into the tank are not toxic. Salt is a good abrasive to scrub many things, driftwood, rocks and other decor. Salt is water soluble, and should rinse clean easily, but a trace of salt that remains is not a problem.
3) Substrate. I would siphon out the water all the way down, stirring the substrate all you can, and adding more water as needed. If you want to bleach it then add the bleach early, and do LOTS of stirring and then rinsing, with a double dose of dechlor in the water each time.
Another option: Before you disturb the substrate, but when the water is gone, use a mist bottle and spray Bleach, Excel or Hydrogen peroxide on the surface where the algae might be. DO NOT BREATHE THESE MATERIALS. Let it sit for a while, then rinse by doing all the deep vacuuming you need to to clean the substrate. Traces of Excel or H2O2 are not a problem if they remain in the tank. Bleach needs to be rinsed with dechlor in the rinse water.
Even more aggressive is to remove the substrate from the tank and treat and rinse in a separate container, perhaps outdoors.
4) Final rinse of everything as you add it to the tank.
5) Put some slow release fertilizer deep in the tank, add some laterite or other material if you want. Do not disturb the substrate deep down after you have these materials in place. Arrange the hills and valleys, driftwood, rocks and so on.
6) Plant, misting often.
7) Refill by placing a plate or plastic bag over the substrate and allowing the water to run in slowly, seeping over the edge of the plate or bag. This will minimize clouding. Add a source of Nitrospira species of bacteria. These are the nitrogen cycle bacteria and hopefully will replace the bacteria you are killing by these extreme methods of algae control.
8) While the tank is filling arrange the equipment, and start it when the water level is high enough. It will cloud because of the Nitrospira additive. This is OK.
9) Net the fish out of their bucket. Do not use the water the fish were in.
Monitor the tank for several days, being ready to do water changes as needed. This has been a pretty complete treatment and will kill off a lot of the nitrifying bacteria on all the surfaces in the tank. It may take a few days for the Nitrospira to attach to things. Do not do a water change in the first few days if you added such a product. Follow the label recommendations. Minimal feeding of the livestock.