how much salt in tank

Question
Hi Chloe,
 I have several test kits and have my water checked at my LPS regularly, everything reads normal. The tank is cleaned and maintained regularly. I belive the ich came from a new addition I foolishly did not quarantine and was first to show symtoms. I have an air stone and a bubble wand. It is an Eclipse 39 gal and is over a year old. I have only lost 2 fish since setting it up. I have a secondary filter system also. The question about the salt is how can I tell how much is left in my tank, how do I measure the salt content of my water? I have maintained the salt content by replacing the amount of salt for the water change, but the treatment has thrown off my ability to gage this. Second will the higher temp alone kill the ich?
Elise  
-------------------------------------------
The text above is a follow-up to ...

-----Question-----
One of my fish has ich. This is my second round with this. I have 10 tetras, 1 balloon belly Mollie, 2 Guppies, 2 cat fish with green spots, 2 alga eaters, and 3 stripy fish with long tails (i know thats not a lot of help) One of my cat fish had ich 4 weeks ago. I used a blue treatment, it did not seem to have any effect so I did water changes and through cleanings. Then did a salt treatment and raised the water temp 80f. This seemed to work, the spots fell off and I waited 10 days before doing a water change so the salt would kill the swimmers. Every body looked fine till today and now my Mollies has a spot. Sorry to so long winded but how can I tell how much salt is still in my tank? I need to repeat the treatment but do not want to pickle my tetras.
-----Answer-----
Hi Elise,
You need to check the underlying problem which is most probably water quality. This will cause stress to the fish and then the ich will infect the fish. Using salt at 1 tsp per two gallons many help. You could up the temp a little more to about 82F as white spot cannot tolerate this kind of heat. Remember to add an airstone because warmer water has lower oxygen levels.

Regards,
Chloe.

Answer
Hi Elise,
Usually when you do a water change it just dilute's the salt so there is no need to keep replacing the salt as it will still be effective. The high temperature will kill the ich but it will only be a temporary solution. The best way to get rid of ich is to do what you are currently doing now.

Regards,
Chloe.