1. I just add it to the tank.

2. They're not going to stop doing that, trust me! You can't spay or neuter a fish. If you have a male and female molly, chances are they will breed. Mollies are prolific breeders. You can pull the mom out and put her in a breeding net before she has the babies. Or you can put a lot of plants in the tank, and some of the babies will hide and make it. That's why I have only male guppies and only male mollies.

3. Plastic are better if you are a beginner. Live plants create a more natural, healthy environment ... but only if you know what you are doing with them. Otherwise they'll die and create a big mess in your tank.

4. I personally test and regulate my PH, but our water is VERY alkaline here. You also need to get a nitrite/nitrate test kit, and an amonia test kit. Frankly, if you set up a brand new 15 gallon tank from scratch on Valentine's day, and already have seven fish in it, you are very likely going to have some serious new tank syndrome problems in two weeks to a month. I would advise you to talk to someone knowledgeable at a GOOD pet store, and invest in some nitrate/nitrate and amonia neutralizers. You're probably going to need them.

5. Bala sharks are peaceful, schooling fish. They should be fine with guppies. Platties and swords are bright orange, and gouramis are many different bright colors. Lemon tetras, neon tetras and rosy barbs are colorful as well. However, I would not advise you to add any more fish to your tank for a couple months.

6. I have a 55 gallon aquarium with mollies, guppies, betas, black fin sharks, upside down cats, gouramis and several types of tetras.