First, I am writing this post because I sometimes keep large baits (bluegill, bullheads, chubs, etc) in my bait tank for long periods of time (6-9 months). I had a friend recently try this and all his died in about a month and he was very frustrated and couldn't figure out why, so here are the suggestions I gave him: First, if you are going to set up one of these tanks do it a month before you plan on putting the fish in! To keep the bullhead healthy and alive you will probably need to fishlessly cycle it. What this means is that you are building up amonia eating bacteria that will break down the very harmful amonia waste that bullheads will create. It is relatively simple. Just add some bacteria (can buy a bottle for about 6 bucks at an aquarium store) and add it. Then add a dead shrimp or other dead fish to give the bacteria some amonia to eat. Then let the tank run and you are pretty much done. You can also buy 100 percent pure amonia and add to the tank and that will lower the time it takes. A general rule: the smaller the tank, the longer it takes (kinda backwards to normal thinking huh) I fishlessly cycled a 10 gallon aquarium one time and it took almost 3 months. NOTE: If you do not want to wait that long or buy the bacteria find a friend with a very healthy aquarium (make sure he/she has fishlessly cycled) and take some gravel, an old filter, scuba diver etc and put it in your tank. This stuff is packed with bacteria and will greatly reduce the time it takes to build bacteria. Another important thing, if you plan on keeping bait alive for longer than 3-4 days, an aerator will not be enough! This gives them oxygen but does not clean the water. You will need a filter. I had an old one laying around from an aquarium that I use, but if you need to buy one here is a good one that is inexpensive. It is recommended for 75 gallons, but you might be able to get away with it for up to 100 gallons. It cost 38.00 bucks and will last for years. http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3579+12320&pcatid=12320 You can buy a much better filter (wet/dry filters can easily run 400 bucks) but that is overkill for baitfish. Go with the Bio-Wheel! Now your tank has bacteria, a filter, and hopefully some baitfish. How about cleaning? I have read on here that people do water changes of 50 percent every 3-4 days. That is not needed. I only change 10 percent water weekly in my aquariums that require much more attention than a baittank. You can probably do 10 percent every other week, as long as you take the right water. Get a cyphon and when you take water, get it off the rocks. This will help remove fish waste. The cleanest water in a tank is the water on the top, so just scooping this out does not help too much. Get to the bottom of the tank. So on a 100 gallon tank, 10 gallons of water change weekly, or bi-weekly should be fine. Any more than that can actually be harmful because of the big fluctuations in pH that can occur (not as big of a deal with hearty baitfish). Also, many people change filters too often. Only change a filter when it is about ready to fall apart! A filter is the number one source of bactiera in an aquarium. When you do a water change, just take the filter out and shake vigorously in the water you are throwing away. When you do think you will need to change the filter (probably once a year) think ahead! Add the new filter to the aquarium a couple weeks before you take the old one out. if you can get them both in the filter, great! If not, just lay it in the tank. Some other notes: This bacteria that I have talked about is vital to a healthy environment for fish to live in (I have no problems using fish as bait, but I feel they should be treated ethical and humanely in the meantime, and this means not having them die from chemical poisoning). This bacteria will do much better with the more surface area you give them to live on. You can add gravel or other things to add surface area, but I just add larger (about 1 pound) rocks. This gives the bacteria surface area but also is alot easier to remove if you are cleaning or need to get it all out. Well this post got a little long. All this stuff might seem complicated but it is all very easy actually, and alot of it makes caring for a bait tank alot less time consuming. I mess with mine (once I have it set up) for maybe 20-30 minutes every other week, which gives me more time on the water! Hope this helps!!!