1. Welcome to my life. My gh is low too and my kh is non existent,but that's the nature of the water here in melbourne, and i think it's much the same in eastern australia. My question to you is what makes you feel the need to change it? Unless you have a specific reason (such as breeding) there shouldn't be a need to try to shoot for "ideals" and you're far better to work with what you got. As long as things are stable, your fish will be fine. Chemically or other manual intervention of these things is fraught with danger.
not true. Fish, especially young ones, need some hardness to the water in order to grow properly. It's actually been suggested by jack wattley to grow out baby discus in well water that is hard in order for these "soft water fish" to maintain an ideal structure. The low gh may be exactly why her snails aren't living for long in her tank. A higher kh is generally better as it prevents deadly, massive ph swings. A lack of kh is setting your tank up for failure. Adding baking soda will increase your kh. Adding a product like kent ro right will increase your gh.
2. What's the "right" level? There are ideals for some situations but as i said, you are better off working with what you have and if you don't have a problem, you don't need to fix anuthing. This is very much the case with ph too. Don't mess with it if you don't have to.
that's the thing! If she doesn't adjust her kh her ph is far more likely to change and cause catastrophe. Imo something should be done...add baking soda.
3. Would want to know your other water parameters. What kind of snails are you buying?
all snails need calcium to build their shells as far as i know. Since gh is a test for calcium and magnesium and her gh is low, this indicates there may not be enough calcium for the snails to build their shells and stay healthy.
4. If it's white salty-looking stuff, it's fine. I have a sponge (chucks super wipe) i use exclusively for the tank. As it builds up, you can wipe it off.
it could be nacl or lime. I'm guessing it's lime, which is calcium carbonate. I'm sure calcium could be harmful to fish in extremely high levels but you would have to add lots of it to the tank in order for it to be harmful. As i've stated already, it is beneficial to snails for shell building and fish for bone growth. It is something that needs to be present.
5. If you're not using any fertiliser atall, you will need to. Just like garden plants, aquatic plants need food. At the minimum you will need a macronutrient fertiliser such as seachem comprehensive or dinosaur pee from aquagreen. Dose as instructed. If you have basic gravel and stem plants you might also want to suppliment this with root tabs which are tablets you bury in the substrate where the roots of the plants are.
why add fertilizer at this stage? We first need to know what type and wattage of lights she has on the tank and what size it is. I'm guessing she has anubias/crypts on the driftwood, which are all lowlight plants and would do well in almost any light. The "bunched plants" she most likely has are medium-higher light plants and they obviously don't do well under low light conditions. Adding nutrients does nothing if the plant can't use them due to a lack of light.
another factor here might be the gravel itself. If it's too large or too coarse, you might struggle to grow anything.
not true. All the gravel does is anchor the plant. Many people use pool filter sand as a substrate in a planted tank and it does nothing but anchor the plants...it provides nothing the plants can use. Some substrates are designed for plants and are rather coarse. I know of several people and have seen in a lfs where they use "river rock" substrate in a planted tank with good results.