Here's a recommended treatment that I got from Tom and Nevin Baily that has worked well for me in the past.
1. Clean/power siphon the tank and gravel (removing and replacing up to 20% of the water). Don't go crazy, just do a regular cleaning, including brushing out siphon tubes, etc.
2. Remove activated carbon and add an anti-parasitic medication like QuickCure (available at Wal Mart) per the recommended dosage for the recommended number of days (at least 4) until the signs of ich are gone.
3. On day 1, also add 1 tablespoon per 5 gallons of water of Aquarium Salt (also available at WalMart). Dissolve the salt in a glass of aquarium water and pour it over the tank.
4. Raise the temperature in the aquarium by 4 degrees over 24 hours. (To a maximum of 82). This will speed up the life cycle of the ich. They are only vulnerable to the QuickCure in the brief free-swimming stage of their development.
5. Change 20% of the water in the tank every day, before adding that day's quick cure. This will help remove any built up contamination in the water and will also immediately start to reduce the salt content from the salt you added on day 1.
The advice you received on pH above is absolutely correct. pH changes stress fish. Change the pH no more than .5 up or down in any 24 hour period. If the fish are sick, try to keep the pH stable.
The salt will work in combination with the QuickCure to attack the parasites and will help the fish to heal. It's not the salt content itself that helps, it is the quick CHANGE in salt content that does the trick. The parasitic organisms don't adapt well to rapid changes in salinity. Further, with the daily 20% water changes, the salinity will soon return to near normal before it has a chance to really make your plants unhappy.
After all the signs of stress and disease have disappeared and your treatment regimine is complete, do a 20% water change and put fresh carbon in your filter.
Use the tests below and continue daily 20% water changes until your aquarium water passes all of them...
Some simple tests of water quality:
Observe how long bubbles remain on the surface of the water before they pop. If they don't pop quickly, do daily 20% water changes until they do pop quickly.
Smell the water. The odor should be very mild and only slightly musty. If the odor is pungent, continue daily 20% water changes until the strong odor subsides.
Place some aquarium water in a clear glass beside a clear glass full of tap water. Observe under good light. The color and clarity should be virtually identical.
Multiple 20% water changes are less stressful on your fish and on the tank's "good" bacteria colonies than fewer large water changes.
Don't base your 20% calculation on the "rated" size of the aquarium. Substrate, plants, ornaments, and fish all displace water. My 135 gallon aquarium, for example, really has only 110 gallons of water in it when it is full.
Calculate 20% by measuring the distance from slightly below the top of the gravel bed up to the water line. Measure down 1 fifth of this distance from the water line and put a piece of Scotch tape on the outside of the aquarium glass so that the top of the tape marks the spot. Siphon the water down until the water line is at the top of the scotch tape and you've removed 20% of the water.
Continue to do daily 20% water changes until your water quality passes all these simple observational tests. Afterward, 20% changes twice a week (as part of a regular cleaning program) should keep your aquarium water in top condition. It will also help keep your fish happy. And, as we discussed in another thread
, plants seem to LOVE partial water changes as well!
Best of Luck!