"My views toward salt are very simple... Don't use it unless you need to. When you do need it, use it in the right amounts. And finally, don't believe that salt is a miracle cure for everything. It does have it's limitations and it's up to you to monitor the progress of your sick fish and decide if more potent meds are needed to help your fish recover.
These are the reasons why I like salt:
1) It does not hurt your filter (will not kill your nitrifiers)
2) Carbon does not take it out of the system
3) If you have a UV system... you don't have to turn it off.
4) Its VERY cheap... doesn't cost a fortune to treat a 100+ tank
5) Will not push very sick fishes "over the edge" like many meds
6) Can be used on most fish species that are sensitive to meds
7) Is not carcinogenic like a lot of meds out there.
8) Has a relatively wide margin for error in dosage
9) Found almost anywhere
10) Versatile... can be used as a long term bath (2 weeks) or a short term dip
What salt will do:
1) Relieve nitrite poisoning (Brown Blood disease) by displacing nitrite ions away from gills membrane.
2) Eradicates a large number of external parasites including ich, chilodonella, costia, trichodina, oodinium (velvet).
3) Combats bacterial, fungal infections and ammonia burn.
4) Kill all salt sensitive plants in your tank (watch out for this one )
5) Recharge ion exchange resins (ammo-chips, water softener "pillows")
6) Can be used to disinfect a used, empty tank by apply it as a "paste"
7) Ease osmoregulatory stress... but only happens when fish are dumped from water of one osmotic pressure into one which is very different. This problem is not a concern because we are dealing with FRESHWATER fishes. Exception is when the fish has a very serious open ulcer.
Salt is NOT effective in:
1) Treating fish lice (argulus), anchorworms (lernea), skin and gill flukes, internal parasites.
2) Replacing electrolytes and trace minerals (unless you are using a marine salt mix which also has buffers that will increase your pH).
3) Treating viral infections
4) Iodine from table salt will NOT kill your fish. The low levels present in table salt will not reach toxic level, even at treatment levels. Your fish will die of osmotic shock or high salinity way before iodine becomes toxic. If you are still not convinced, cheaper alternatives to aquarium salt are non-iodized table salt, kosher salt, water softener salt (Home Depot sells 40 lb. bags for under $5 that are 99.8% pure NaCl).
All that being said, I don't believe that salt should be constantly used in the aquarium as a general tonic. They are freshwater fish and should remain so.
How to administer:
There are many "Rule of Thumb" guidelines for how much salt to add. Either, 1 tablespoon per 5 gallons, 1 tbsp/10 gallons, etc... If this has worked for you in the past, fine. I have always dosed my tanks at 0.3% (3 tsp/gallon) when needed, which is considerably higher than many suggest. Only exception to this rule is for nitrite poisoning where a teaspoon of salt will treat over 300 gallons of water. Many believe that the constant use of salt in low dosages is the reason why we are having problems with salt resistant parasites. And as a result, some parasitic infestations need to double the dosage to 0.6% to see any significant improvement.
My recommended dosage, even for ich, is 0.3% (which is a TOTAL of 2.5 lbs/100 gallons or 3 tsp/US gallon). The amount of salt added should be done in 3 equal increments over 3 days and left in the system for 2 weeks (that's 1 tsp per gallon per day for 3 days), in which time, the salt should be taken out through water changes. ALWAYS pre-dissolve the salt before introducing it to your tank! Measure out the desired amount of salt, add aquarium water to a bucket or cup (I use a 44 oz plastic "Big Gulp" cup) and stir like crazy until the salt dissolves. Slowly pour the salt solution into the tank and make sure you are not pouring it on top of your fish. I prefer to pour the solution in the path of a powerhead to help distribute it throughout the tank. A "blast" of concentrated salt solution may cause severe burns to your fish. Therefore, NEVER add salt directly to your tank.
For salt dips, a 1% solution (9 tsp/gallon) can be used for around 10-15 minutes and then the fish is returned back to clean aquarium water. For extreme cases and as a last resort, a strong 3% salt solution can be used. The fish must be constantly monitored and is basically kept in the bath until they roll over and is transferred IMMEDIATELY back to the aquarium. Fish will try to adjust to the changing salinity and the longer you wait, the more adjustments the fish needs to make. I'm not a big fan of salt dips because they are very stressful on the fish.
One final note, livebearers and cichlids will tolerate much higher levels of salt than many other freshwater fishes such as characins (tetras), loaches, and catfishes. So this practice is not recommended for all species."
