I wouldn't put it in the aquarium. The reptiles can tear up your plants, defecate/urinate on them, and otherwise kill them. As others have said, more light is needed for certain. You can try to kill the mold with things like CP-safe fungicides, but it can harm your plant and is only a temporary measure at best. The mold will inevitably come back no matter what you do unless you improve your conditions. Your water levels are probably not the problem. Your plant (Drosera spatulata) is tropical and grows year round so you do not need to change the water level.
In addition, the rotting sundew that you observed along with the mold indicate that your soil is probably decomposing or has contaminants. The clay pot might even be leaching chemicals into the soil, as previously mentioned. Repotting it into fresh soil in a plastic pot will solve this. (I would recommend planting it in something like 50/50 peat/sand or peat/perlite, since it looks like its growing in pure peat right now).
Overall, your light is the main problem that needs to be solved. It doesn't matter that it is fall right now, your plant needs more light and will continue to decline unless you give it more light. If you can't get anything else right now, you can use a desklamp to supplement light levels.