I have heard about adding salt to my pond. What is the purpose and when should I do it? Also, how much do I add, what type of salt is used and is it harmful to my plants?

Salt is a general antiparasitic and the fish do better with a little salt in the water. The reason for this is a little complex. All fresh-water fish expend a great deal of energy maintaining their internal salt concentration at a level very similar to ours. To do this, they must pump free water out of their systems and hang onto every molecule of salt they can. They fight this constant osmotic battle with their relatively salt-poor environment every second of their lives. When a fish is under stress (poor water quality, infection, injury, low oxygen, transport, high temperatures, predation, pollution, etc.) energy must be diverted from this effort to combat the effects of the new stressors. If these energy demands exceed the fish's energy reserves, it loses control of its internal electrolyte balance, becomes edematous (dropsical) and dies. The addition of salt to the pond lessens the energy demand on the fish needed to maintain its osmotic balance, leaving more energy reserves available to grow, fight off parasites and other infections, and heal injuries. Salt also specifically blocks the binding of nitrite to the hemoglobin molecule in fish blood. It prevents "brown blood disease" and is especially useful when a new biofilter is being started up, an old one is being restored following a "crash", or an established biofilter is restarting in the spring.

One caution. If any part of your filtration system uses the ammonia-binding chemical sold under the trade name "Zeolite" do not use salt! On contact with salt, Zeolite promptly releases all the ammonia it has captured back into the pond, and will remain incapable of resorbing the ammonia as long as the salt is in the system. The only way to remove salt from your pond is water changes. Lots and lots of water changes. (No, you can't throw potatoes into the pond and expect them to suck it out!)

Many of our members salt their ponds year 'round. Many do not salt at all or only when they have problems with parasites or nitrite load. Pond plants will tolerate salt levels up to 1.5 lbs/100 gal water. The best salt level for disinfection in a pond is 2.5 lbs/100 gal. For individual treatment, try "The Dip": brief immersion of your fish in a heavily aerated salt solution at a concentration of 2.5 lbs/10 gallons. (Take your fish out when he starts to tip over. This is a *major* stress!) We salt our pond in early Spring, before any of the plants are awake to the 2.5 lbs/100 gal level, then bring the concentration down slowly to between 1.0 and 1.5 lbs/100 gal as the season progresses and the plants start to appear. Remember do not use your salted water to fertilize your lawn!

(Answer courtesy of Bob Passovoy)