Where is the algae located in the tank? If on the glass, you can use a single edge razor blade to remove it; if on acrylic, you can use a soft cloth or special algae scrubber made for acrylic tanks. Some people also use Original Magic Eraser to remove algae from hard surfaces though be sure to buy the kind without soap or additives.
Hard water is usually not a problem for snails so it might have been the Julies. What species or kind of snails did you buy?
Technically, you don't NEED an algae eater... though maybe you want one. The fish will be perfectly happy in a tank, with the rocks etc, covered with algae, in fact it will be healthier for them, and their babies. If it's on the glass, it's best for you to clean it anyway.
Most effective algae eaters, will end up trying to eat the eggs and/or fry of the Julidochromis anyway. (So I'd avoid them).
If the algae is an ongoing, persistent issue, you might have too much food, not enough water changes, or the lights are on too long. (If it's a long-time established tank, some new tanks go through an algae phase, that can be eliminated with a couple of water changes, and reduced light)