Net – For catching fish that need to be moved. But ideally you shouldn’t be moving your fish around any more than absolutely necessary.
Thermometer – Keep a close watch on your tank temperature. Even if you have a heater, don’t assume anything, many fish have been lost to a heater malfunction. Personally, I don’t use heaters. Most fish will do quite well with the normal household temperatures of from between 70 – 82°F.
Gravel Vacuum – One of the most important items in the Aquarist tool kit. Use this wonderful syphon to clean the gravel in your tank. It’s not just for tanks with an undergravel filter. In fact a tank without an undergravel filter needs it’s gravel vacuumed even more. They are much more prone to having pockets of anaerobic (bad guy) bacteria because there’s not a constant flow of clean well oxygenated water moving through the gravel bed.
Algae Scraper – To keep the glass free of unwanted algae. I only scape the front of my tanks. Algae is not a bad thing if kept under control and in fact adds oxygen to the tank as well as feeding off of the excess nutrients available in the water.
Bucket – A 2 or 3 gallon bucket dedicated solely to aquarium chores. Never use any soap or other chemicals in your “aquarium” bucket. This will come in handy for the water changes and other wet chores associated with aquarium keeping.
Dropper / Feeder – I use a small eye-dropper type tool to feed my fish frozen and live foods. My “dropper” is actually a automotive antifreeze testing tool. Of course never use a used one. It is just the right size, where a eye dropper was too small and a turkey baster was too large.
Table Salt – Iodized or not, the amount of iodine in table salt is negligible. Salt is a wonder drug for freshwater fish. Many diseases can be cured and / or prevented with the simple addition of a teaspoon of salt per gallon of aquarium water.
Timer – A timer for your aquarium lights will definitely be a great time saver. Keeping the lights on at a consistent time will benefit your fishes health. After all, how would you like it if the sun came up an hour or two earlier or later every day.