Hello, I have a couple of questions regarding the stocking of my fish tank (20 gallons). Currently I have a shoal of six neon tetras, 3 balloon mollies and 1 gold dust tail molly. I am going to avoid overstocking but I still need to get a scavenger. My questions are:

1. What is a good scavenger fish/invertabrate for my situation?

2. After I get that scavenger fish/invertabrate for my tank, would I have room for any
more fish? (Algea eater in particular.)

Other things I was hoping could be answered:

3. When researching how to preform my filter changes, I have been getting contradicting answers. Should I change the filter packet itself every month? Or would that be taking out to much beneficial bacteria? If so would it be better to "rinse" in old tank water then completely change it every few months? I could really use an in depth answer here as to how to go about rinsing in old tank water and that whole process if that is the way to do it!

4. I do not have any real plans as of now to switch my tank to a planted tank but I might be interested in doing this a while from now. My question is, would a normal gravel substrate work or would I need to switch to a different kind, (like a soil). What type of light would I need? Is there anything else needed to take care of the plants?

Thanks a lot for helping me. Im only about six weeks into my fish tank and I just want to make sure im prepared for everything!

1. What do you mean by scavenger fish? Are you looking for a bottom feeder? Cories are nice, but need to be kept in groups of 5 or more. As for inverts, amano shrimp are fun.
2. depends.
3. What type of filter are you using and what filter media? At least a part of your filtration should be biological. This would be a sponge or a wheel or ceramic tubes--something that the beneficial bacteria can grow on. This should not be replaced EVER, unless it is literally falling apart. If it becomes gunked up, you can rinse it out. Many people use old tank water because the chlorine that is in most tap water will kill the bacteria. A technique that i use is to use conditioned tap water that is about the same temperature as my tank.
4. There are some plants that are very hardy that do not require anything special in the way of lights or substrate. On the other hand, you could spend hundreds of dollars on lighting, pressurized CO2 and fertilizers. Depends on which route you want to go.

1. Cories sound like a good idea but if i need to get a group of five.. wouldnt that put to much of a bioload on the tank?

2. Lets say i got cories, would i be able to get a small pleco, like an albino bristlenose? If so, after that would my aquarium be fully stocked?

3. My filter is a HOB that came as a kit with my aquarium. It is an aquenon whisper filter but on the instructions for changing the cartridge, it says that it has a bio slot and a cartridge slot. It said the bio slot is where the beneficial bacteria goes so if i change the cartridge i should not be affecting the bacteria... does this sound correct?

4. Sounds pretty easy. I might try some easy maintainable plants some time.

Thanks for the replies so far!

Ok thanks for the replies everyone! It was very helpful.