Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
A move to a new water district can be really hard for the fish. Added to the stress of the move is also the change in mineral content in the water. Fish can handle small changes in mineral levels, but larger changes need to be accomplished over several weeks or a month.
If you saved a lot of the water and the fish are in perhaps 75% old water and 25% new water the mineral levels may not be causing the problems. If you have remained in the same water district, same pumping station and so on, then the water is probably the same in the new apartment, and, again, mineral levels are not, in themselves, the problem.
However! Shimmies and lying on the bottom sounds like a change in mineral levels in excess of what the fish can handle. This may be triggered by stress. Fish under stress osmoregulate poorly, and even if they are in the same water they are acclimated to problems that look like mineral level issues can happen. Also, Mollies are hard water fish. If they were in water that was already pretty soft, then the new water is slightly softer, this can cause problems. It may be below their tolerance level for GH and TDS.
I would add salt to the tank (or remove the Mollies to a quarantine tank) at the rate of 1 tablespoon per 5 gallons. But do this slowly, and watch the fish.
Try 1 teaspoon per 10 gallons (dissolve in some water, pour it in), let it circulate for an hour, then add another teaspoon per 10 and so on. If the fish seem to recover sooner, then stop adding salt. If you need to keep adding salt 6 times (6 teaspoons per 10 gallons is the same as 1 tablespoon per 5 gallons) then stop at that point. This level of salt is not good for aquatic plants.
If you can get water tests of the old water and the new you can adjust the new water to be closer to what the old water was like. Do you still have any of the old tank water before mixing it with the new water? To raise GH in an emergency you can add Epsom salt. To do it right use Barr's GH booster. It has more of the minerals that are needed in the right ratio.