What "chemical" did you treat this tank with?
Also, an anemone is an invertebrate, thus your tank is not FO--fish only. In the hobby, FO means that you have only fish in the tank and no inverts, live rock, live sand, corals.
If you put a chemical in the tank, this could have effected the anemone [not to mention the fish]. How is the anemone doing?
Also, what are your water readings? It seems to me that your tank is overstocked for a 2 month old tank.
Do you have a separate hospital tank? Since we don't really know if your tank is really FO [minus the anemone] it is hard to advise you how to proceed. You can not treat using hyposalinity [or any chemicals or drugs for that matter] in a tank that has inverts, LR, LS, corals.
Here is the procedure for hyposalinity:
O.S.T. stands for Osmotic Shock Therapy. No, your fish aren't subjected to the shock, but the parasites are. Essentially, O.S.T. simply places the infectors in an environment in which they cannot hope to survive while the host, (or infected fish) can. This remedy WILL NOT work in reef systems or invert tanks as it incorporates lowering the salinity of the entire system to below what is tolerable to reef systems or inverts.
To drop the salinity you do water changes—replacing salt water with fresh. Monitor the lowering closely so as to not reduce it too fast. Usually over a period of 48 hours is fine. The bacteria colony will survive, the fish will survive, but the ich will not. By lowering the salinity, you will also be lowering the osmotic pressure of the water. The parasites NEED high osmotic pressure to convert saline water into freshwater. All marine animals need freshwater as we do. They just convert it differently, usually via their tissues. Reduce this necessary pressure and the ick parasites will die. As a higher life form, the fish can withstand this treatment very well. Inverts and corals cannot!
Your goal is to drop the specific gravity to 1.009 [over 48-hrs] gradually. Once all signs of the parasite are gone, then keep your fish in this hypo-saline water for 4 wks. If all is well, then you can gradually [over the course of 4-5 days] bring the specific gravity [salinity] back up to normal levels. If you are using a hospital tank rather than performing this treatment in a separate tank [recommended] then leave the fish in the hospital for another wk with the salinity at normal levels. If all is well after a week, then return the fish to their main tank.
When the fish are eating, offer them quality and varied food soaked in garlic. Since you have tangs, they need good sources of vegetable foods because these are vegetarian fish.