Salt Against Ciliates
I recommend that you use salt, before you try anything else for parasites. I recommend salt so often because it has so many benefits over other mendicants’.
Namely:
1) It does not harm the majority of fish species.
2) It does not push sick fish "over the edge."
3) It eliminates, QUICKLY, 7 of 9 parasites I can easily recall.
4) It does not get bound out of the system by organics or sunlight.
5) It does not pose a health risk to humans contacting it.
6) It is CHEAP, CHEAP, CHEAP.
and 7) It WON'T harm your filter!

Salt: Remove submerged plants. Perform a fifty percent water change, and clean the pond as well as reasonably possible without causing undue delay in treatment.

Apply one teaspoon of non iodized table salt per gallon of water every 12 hours for three treatments (3 tsp per gallon).

Alternatively, for larger systems, dose one pound per hundred gallons of water every 12 hours for three treatments (3 pounds per hundred gallons).

Add all at once in the case of epidemic mortality.
Salt is a superior remedy for many different reasons, many of which will show up in a search of this website. Kosher salt, Sea Salt, Non-Iodized Table, Rock and Ice Cream Salts are acceptable. Do not use salt intended for livestock if it contains any minerals or trace elements.

Caution! No YPS or Yellow Prussiate of Soda should be in the salt. Prussic Acid is hazardous to fish because it dissociates into Prussic Acid in water!
Add the salt all at once if fish are dying off rapidly
Add one pound per hundred gallons, per day, for three days if fish are merely sick. This avoids occasional filter-shock. (2-3 day nitrite spike)
Will not harm hardy Lilies, common Papyrus, or Irises. Will cause yellowing of Hyacinths, Celery and Water Lettuce, but will kill Anachris, String Algae, Cabomba and Elodea.

Strengths
3 pounds per hundred gallons = 0.3%
6 pounds per hundred gallons = 0.6%

Pull sensitive plants to baby-pool and treat with Formalin in this. (25 ppm 8-12 hours)
Leave salt in the pond for 14 days minimum, then remove by partial water changes over subsequent weeks.

Note From Doc Johnson
"I am always absolutely sure to read every ingredient in the salt I am using. I do NOT take it for granted tha my time honored favorite brand of salt is still being made with the SAME anti-caking agent as always. 

They *do* change these ingredients occasionally and the addition of Yellow Prussiate of Soda (YPS) can cause death fairly rapidly in soft water!"
Astor, Akso, Diamond, Nobel, or Morton brand non-iodized salts sufficient to treat one system to 0.3% two times. Most any salt is okay if it's not: YPS laced, mineralized, iodized, or really dirty. I've used animal feed or licks - "salt blocks" from the feed store with excellent results, you need to read labels and look for 99.5% purity with no trace minerals. The blocks are easy to store and transport. Put them in the way of the water return and they dissolve rapidly. NEVER put salt into the filter intake. The sudden rise in salinity will annihilate your filter bacterial function. One man local to me put fifty pounds into his skimmer, straight through the filter, and made his beads snow white.

What's the "scoop" on iodized salt; is it toxic or not?

Not toxic to fish. Very likely, the first few times it was used with smaller filtration systems in higher amounts, it set the filter back causing an ammonia situation to arise. It was theorized that the bacterial stumble was caused by the iodine/betadine effect.

Salt can be used in freshwater systems by adding one teaspoon of salt to each gallon of water every twelve hours for three treatments. You are gradually increasing the salinity to a level of 0.3% or three teaspoons per gallon total. The dose goes in gradually over 36 hours to avoid shocking the filter (especially Nitrobacter, which results in a short Nitrite surge). Some sensitive fishes will also do better when salted if it's added so gradually.

Salt should be of the table salt variety, or an Aquarium salt recommended by the Pet Shop. Live plants can be killed or yellowed by this, so be careful to remove these before treatment. As a general rule, plants with a defined root system will usually survive salting, while floating varieties like Anachris, Cabomba and Wisteria are flatly killed. My Apons died back 50%, Cryptocoryne couldn't care less, Pennywort hated it but did not die, Anubias yellowed and recovered, in the ponds, Lilies yellow marginally but do not even stop flowering. Iris is impervious, and Hyacinths hate it but they only yellow in the older leaves, and bounce right back.

Is there a way to measure the salt once added?
Yes, there are electronic salt meters which are accurate, easy to use and surprisingly cost effective.

What can salt do for me?

Salt at 0.3% is credited with the clearance of the following:
Ichthyophthirius (72 hours at tropical temperatures)
Chilodinella (24-36 hours)
Costiasis (Ichthyobodo necatrix)
Almost every single Trichodiniid/Tripartiella organism.
Glossatella (24 hours irregardless of temp)
Scyphidia (24 hours irregardless of temp)
Epistylis (24 hours irregardless of temp)
Trichophrya (24 hours irregardless of temp)
External Tetrahymena
Inhibits trematode reproduction, clears 30% of adults.
Inhibits Lerneiid reproduction

UPDATE: Because the abuse of the overuse of salt, we now have many "salt resistant" parasites such as: ich, costia and others. The product TERMINATE will treat "salt resistant" parasites. 

How long do I leave it in the water?
Fourteen to 21 days may be required to totally eradicate certain parasites at certain temperatures. Rest assured, it could stay in the water forever. But for Ich it could also be removed within seven days and recurrence of Ich would be unlikely if temperatures during treatment were around eighty degrees F. Ten to fourteen days is suggested 'for best results' with Ich.

Removal is by simple partial water changes. Be careful that the effluent water is not wasted onto a precious Japanese Maple or your Dad's best Bermuda grass as it could do it some damage.
I traditionally use salt for most protozoan parasites, especially Ich. I use salt because so many other medications for Ich are caustic to the fish, reduce dissolved Oxygen levels, and can tend to disable the filter bacteria that remove Ammonia.