I don't use stress coat, only prime as a water conditioner but I don't see how it would be a problem.

 

I've also used melafix before, and successfully, by using a portion of the dosage for my betta, for a short time, but generally, depending on what's wrong, it's not my first choice. As for using it with stress coat, I used it with API's Stress Coat+ and it worked just fine, no harm in mixing the two that I know of.

 

How do I mix the two? The dosage that it suggests? Or Half and half?

 

well.. since your stress coat is basically a water conditioner with the added slime coat support, use it as directed based on your tank size, when you change the water. The melafix... I put no more than five drops out of my bottle in per day, usually doing daily or every other day water changes (in a 1 gallon hospital tank). You don't want to half and half the dosage of the stress coat mostly because it's not a medication, it's a conditioner for the water that helps to relieve stress for the fish. it doesn't go away and only needs to be added when the water is changed, or if you add new fish and you want to make sure the new fish don't get stressed.
The melafix IS first and foremost a medication, so that you can do once a day for a sick fish, try to do it about the same time, and keep the dose smaller, simply because too much of it CAN do more harm than good, but small amounts (in my experience) is alright.
I wouldn't reccommend long term usage of it, as a staple tank additive for a betta, simply because long term it can do more harm than good. It's a good medication, but it can be harmful over a long term exposure.

[on that note, I apologize if I sound like I'm lecturing, but I really wouldn't use it long term]

 

API Stress Coat contains" aloe (Aloe barbadensis), a chlorine and chloramine neutralizer, and water. API's Material Safety Data Sheet (MSDS) doesn't list the specific ingredient that's used to neutralize chlorine and chloramines, but it's likely to be sodium thiosulfate (Na2S2O3).*

As Fishehgobloop said, API Stress Coat is a water conditioner. It's used to treat your tank water, and should be used according to the instructions on the label.

On the other hand, Melafix is a medication.* (The active ingredient is listed as cajeput oil.) If you choose to use it, you'd add it to previously conditioned water.

There shouldn't be any issue with adding the medication to the treated water. The Stress Coat's ingredients (aloe, sodium thiosulfate and water) won't "interact" with the ingredients in Melafix (cajeput oil).

* Sources:
1) API Stress Coat MSDS: http://www.apifishcare.com/products/msdss.aspx
2) Aquarium Wiki which says API Stress Coat uses sodium thiosulfate, and provides a reference to their source: http://www.theaquariumwiki.com/Water_conditioners
3) Melafix MSDS: http://cms.marsfishcare.com/files/msds/melafix_111909.pdf

 

There shouldn't be a problem.

 

No it wasn't lecturing. It's when people tell me all together not to use it and state what they've heard rather than what they've experienced that bothers me. Or get mad for using it. I only plan to use it when she needs it. She's almost fully recovered and then she can play with all the other girls. I don't use it if they don't need it.