"I have two 55 gallon tanks. The goldfish tank has 4 fish the longest being 4' body and I haven't lost any of them. Yesterday, I tested with strips, had nitrites = 10.0 nitrates =40. I did a 20 gal water change with no difference; did another 20 gal water change 4 hours later and I am at nitrites= 5.0 and nitrates= 20. I plan to do another 20 gal water change today. I am using a Top Fin dechlorinator, but ordered the Satchem product yesterday".

Sweet, two 55 gallon tanks is exactly what I was hoping to hear. When you do a water change you want to make sure you change enough to make the difference. With nitrites of 10 I would probably do 2 back to back 80% water changes. You're just diluting the concentration of harmful elements in the water so if your water change isn't large enough, it doesn't make as much of a difference in the overall chemistry of your tank.

"It has a Tetra Whisper hang on that is rated at 70 gal. I did replace the filters and after doing more research and reading more threads, I see where that was a mistake. I will order the API Master test kit today or do you have another suggestion? Again after more research, I understand that I will have to do daily water changes until it is under control and I intend to do that."

The API Master Test kit was a perfect choice and will be your best friend! Just a heads up that you are going to want to add more filtration to the tank. You will constantly see the recommendation that you add double the filtration capacity for the size of your tank (IE a 55 gallon tank needs 110 gallons worth of filtration) This isn't just that we are being overly cautious. The reason for this recommendation is that when the manufacturer tests the flow rate of the filter they do so without any media inside. We pack our filters with media for our beneficial bacteria to live on thereby reducing the flow of the filter. Especially in your goldfish tank (they are extremely messy). A canister filter would be a great addition to each tank. When you are ready to add filtration, we can give you recommendations, but we'll cross one bridge at a time. Right now we want to get your water chemistry safe for your fish.

"I started with Kordon Rid-Ich Plus-advice from PetSmart. I did a 20 gal water change, increased the heat to 85 degrees, and added an aerator. I didn't seem to be making any difference. So after reading different places on the web, I tried the salt. I have killed off 4 neon tetras in the process. I was thinking that I wasn't going to be able to get rid of the ich, so I would start from scratch, i.e. dispose of the fish, plants, gravel, etc. and cycle the tank the right way. If there is a sure fire way way to be rid of the ich, I am all ears and will try it. As to your plant suggestion, I have plants in that tank now, but not the goldfish tank. I will get some floating plants today for the goldfish tank.."

Honestly, adding treatments and salts in a fish tank is usually a last resort. The best thing for your fish with ich is going to be to kill the ich by raising the temperature. So the first step here is to confirm that it is for sure ich. This article has some great pictures that you can look at.
It should look like someone sprinkled salt on your fish. Once you have confirmed that it is ich, you need to first make sure you have removed all the medication from your tank, then you can raise the temp to 86 degrees slowly. Ich medication and higher temperatures both cause a lower oxygenation in the water. This often accounts for deaths of already weakened fish, so the addition of a couple of air stones would be of great benefit as well

I've rambled long enough and I think you have more than enough to digest right now, so let me know when you test kit comes what your parameters look like, also let me know if you for sure feel like it's ich you're dealing with based on that article that I linked and we can take it from there.