Thank you for visiting my question..

I have two young fancy goldfish Bob is a black moor about 1.5 in, Pearl is a Pearl Scale about 2in.. and of course I have Nascar the snail. I have a 20 gal tank for the moment with a 25 gal biowheel and a airstone. My tank is 0 on the ammonia, 7 ph, nitrite 0 and nitrate just recently is between 5 and 10. I feed them rotating goldfish crisps, sinking min sticks, algae wafers and peas . I feed them usually every other day.. But lately daily, so I think that is why my nitrates have gone up. I also, vacuum and change water filter and do a 20% change every month. When I first got Bob he had mouth rot after almost two months of many treatments it finally went away after giving him Tetracycline. Then got Pearl a month later. Anyway, they seem very healthy and happy.. No big tummy's well Pearl but she is a pearl scale.lol. Don't seem to have dropsy, they are very active and have no noticeable problems.. but they are ALWAYS gulping at the water line.. Why is this and should I be worried?

You are a good fish keeper! Since you have a filter and air stone, you can count out that your fish are gulping for air. You also mentioned that they are active and looking good, so my guess would be that they are looking for food or have developed a little bit of gas.
A goldfish has a digestion track different than most aquarium fish. It is shaped like a straight tube, what goes in comes out very shortly after, leaving the fish hungry.
Round belly fish that are accustom to eating at the surface will always search for food there and while doing so gulp air which leads to gas.
Try feeding your goldfish two meals of peas for a day (thawed frozen peas with outer skin removed) to rid them of any possible gas, then two very small meals of what ever your choice everyday thereafter.
Since you have round belly fish, it's a good idea to always sink your flakes or use sinking types of food, that way they can get into the habit of looking for food at the bottom. These types of fish gulp too much air when eating at the surface and tend to get bloat and swim bladder disease because of it. Feeding the peas are a great way to keep their bellies in good health - good job!
It's always good to have a little Nitrates in the water, this assures you that your biological filter is working properly. You can have up to 40 ppm of nitrates reading in your water and still be in the safe zone. Your bio wheel is great - never clean it either (thats where all the good bacteria live that convert all the fish waste to a non toxic form). Also over cleaning a goldfish tank is a big mistake. You want as much good bacteria living in the rocks as possible to take care of the poop.
When doing your partial monthly water change, change or clean filter pads first, by doing this you will keep the beneficial bacteria from the rocks in your tanks filter - then stir up the gravel (just a little) then change no more than 5 gallons (with a 20 gallon tank). The rest of the Debris and bacteria will settle or be sucked up by the filter.
By cleaning a tank this way, you enable the good bacteria to keep the tank clean for you, the result is crystal clear water that you'd never expect in a goldfish tank.
Keep us posted!!

Can I feed the floating goldfish food to my Fighting Fish, as it sounds like I need sinking food for a round bellied goldfish.

Would the fighting fish you're referring to be Betas?
If so, yes, they can eat floating food, but I'm not sure if they'll eat goldfish food.
It won't hurt to try it.
They love the freeze dried blood worms and they also sell food especially for Betas.

As long as they are doing like you described, I wouldn't worry. And I would check my water temperature.