Hello, and welcome to the hobby, as well as the forum!
The pH stabilizer, I'm sorry to say, is a waste of money. It's a phosphate additive that artificially buffers the pH, while at the same time flooding your tank with phosphates, which isn't a big deal for mollies, but other more delicate fish and invertebrates like shrimp and snails are very sensitive to phosphate. As stated above, it's better to just let your pH stabilize on its own, as many fish (especially mollies and platies and goldfish
) can adjust to a pretty wide range of pH. If you're still dead-set on lowering your pH, consider a mesh bag of sphagnum peat moss (you can find the bags at PetsMart or PetCo, and peat moss in the gardening section of your hardware store) in your filter. Peat is great for adding tannins and lowering pH. But that's not really necessary with mollies, in my opinion.
Also, you should stop using ammo-lock. While it does bind with the ammonia ions and renders them non-toxic, the new molecule is harder to digest by the nitrifying bacteria living in your filter and tank, and in addition the binded ammonia still registers on your ammonia test kit, so it's sorta like a false-positive reading. As stated, if you want to help things out, SeaChem Prime is a great water conditioner.
The ceramic bio-media and your mechanical fiiltration (sponge) are really all you need in your filter, as well, so you can ditch the carbon. Carbon is really only necessary to strain medications out of the tank, otherwise it's just a waste of money. I've been running my 10 gallon for 4 years with no carbon. If you want to add something to your filter in place of carbon, double the amount of ceramic bio-media in your filter, or add a bag of peat moss as suggested above. And don't change it unless it's literally falling apart, otherwise you're wiping out the majority of your nitrifying bacteria colony every time you put fresh media in.
The API Master freshwater
Liquid Test Kit is a great investment, good job on selecting the best out there. The liquid titration you do when you mix the tank water with reagents in the vials is much more accurate than test strips, and you literally bought about 100 tests for $35, instead of 20 for $10 like you would if you bought the strips. The ammonia kit does measure free and binded ammonia, however, so even crystal clear pristine water sometimes gives a 0.25 ppm false reading.
Let us know if you have any other questions, we're here to help!