Your water is 50° right now, which causes a couple of problems. Koi and goldies have almost no immunity at low temps, meaning they can't fight off the parasites. And any parasite treatment (except salt) that is recommended for the treatment of ICH cannot be used in cold water because the formalin in it will turn toxic to the fish in cold water. That leaves only one solution for your fish.....and that is salt. Fortunately, ICH is one of the few parasites that can be treated with salt. Unfortunately, your plants may be damaged or killed, depending on the plant. Some can handle higher salt levels than others. If you can remove the plants to a kiddy pool during treatment, you will be better off.

You need to get your salt levels up to 0.4%. Don't do this all at one time...it is too much of a shock. Add salt over a 3 day period. It takes 4 pounds of salt per 100 gallons to reach that level. There are a couple things you need to do first though. First, clean the bottom of the pond as good as possible. The larval stage of ICH lives in the water and hides in mulm so removal of it is important. Also do a large water change to get as much of the previous parasite treatment out of the pond. No more than 50% though because you don't want to shock the fish too much. Then start adding salt. Get the Solar salt in the blue bags from lowes...it comes in 50 pound bags for around $6. Pond salt or fish tank salt is not necessary...the Solar salt works just fine. The salt level must be maintained for 3 to 4 weeks so whenever you do a water change, add salt to replace the salt lost. This length of time is necessary to kill off all the various life stages of the ICH in the pond.

Good luck to you.

Cindy