I agree with the others, the tank isn't cycled properly. In fact, I don''t think the cycle has even started. Ammonia are the food that your bacteria need to multiply, so if you are using ammo lock, the bacteria are not getting the food they need & are not developing in the first place. You really need to stop with the ammo lock & start doing daily water changes. Over time you will see the ammonia turn into nitrite then into nitrates.
Baking soda is for raising PH & more so, KH. The neutralizer is for doing the exact opposite thing. So you have one additive combating the other. Personally I would stop using both the Baking Soda & the neutralizer. A PH of 7.8 is no problem for most fish, especially if they were bought at an aquarium as the aquarium will just be using straght dechlorinated tap water in their tanks except for species like discus that absolutley NEED thier water a certain way. Why on earth your LFS told you to use both together is totally beyond me. I also can't work out why you would use Baking Soda just once. As soon as you do a water change it will remove some of the carbonates that were added & will do so at each water change there after. If you were to use Baking Soda to give you a higher buffering capacity, you would have to continue it's use at every water change & have added it to the water for the water change before the water is added to the tank. I think your LFS is leading you up the garden path & they should not be trusted at all.
As for the bubbles, it looks like it is foaming up in there so it is definitley from a detergent of some kind or one of the additives you have added. It is possible that your LFS has cleaned the tank out with a detergent as well seeing as they don't seem to know very much about what they are doing.
If I were you I would definitley not be going back to that aquarium unless it was to give the person you dealt with a big gobfull of things not very nice!! I would also follow the advice you have been given by the people on here as it is good advice given by people with plenty of experience & not people trying to make money out of you. These people here know what they are talking about & are trying to get you to have plenty of success. They hate it when things go wrong for other people & will go out of thier way to try to help. Have a read up on the
nitrogen cycle in the forums here abouts, I think it might give you an idea of where you went wrong. I would also be getting the Gibberceps out of that tank as quikly as you can. That's a fish that gets to well over 40cm & is in no way suitable for a tank as small as 20gallons.
Sorry if I sound harsh or abrasive, I don't mean to be. I just want you to do the right thing by yourself & more importantly, your fish.