Keeping cool water in your bait tank is a critical factor in keeping quality bait during the summer months. I generally like to keep my bait tank in the mid-60's to low 70's range when keeping alewives. Ideally you want your bait holding in water that is no more than a few degrees, maybe 5, from the temperature at the depth that the bait is being pulled from, or where you will be suspending it when fishing. If you pay attention to the depths where you mark schools of alewife, you'll typically see them holding from 20-40 feet (or even deeper). Ever notice how you have to catch bait at deeper water lights as the summer progresses and water temperature increases - it has everything to do with the bait pulling back to levels with more comfortable water temperatures (as long as those levels how sufficient dissolved oxygen - but that's a whole other article).
If you have a deep-water well at home, you can fill your tank will well water, but check the temperature as the well water may actually be too cold and you'll need to temper it with some warmer, lake surface water to get the right balanced temperatures. Another thing to watch out for with well water that many have experienced is often water pulled from deep-water wells if low in oxygen, and if you fill the tank and immediately put bait in the tank they may suffocate from lack of oxygen. Therefore, it is always a good idea to run your aerator on the tank for a while before adding bait to a newly filled tank if using well water. Also, to be clear, we are talking about UN-CHLORNATED well water here - city or community water and your bait do not mix unless you first treat it with a de-chlorinator chemical.
OK, but what if you do not have access to a deep-water well at your house or boat dock, so how can you get cool water for the tank? One way is to fill the tank with lake surface water and then cool it down with ice. If you use ice be sure that you use dechlorinated-water based ice. You can by bagged ice at plenty of places around the lake - "Hometown Ice", found around the Smith Mountain Lake are has proven safe, but at $2 per 10 lb bag, this can begin to get costly. In my 40 gal SuperBait Tank II tank, a 10 lb bag of ice will bring the water temp down somewhere around 3-5 degrees. So, if I use surface water that is 80-85 degrees then I'll need at least 20 lbs of ice just to get the tank down to where I want the temperature to be BEFORE I put bait in - much less the ice needed to supplement in the tank throughout the day if I am keeping bait across a weekend.
If you don't fancy all that store-bought ice and want to ensure you have "safe" water, you can also freeze lake water by filling some soda bottles or tupperware to freeze blocks of ice and then putting the blocks of ice and/or floating the bottles in the tank, but this creates the hassle of filling your containers, freezing them in a deep-freezer, and then transporting the ice to your tank.
Isn't there an easier way that prevents lugging around coolers full of ice? Well, we want to keep our tank water around the temperature that our bait is coming from - so somewhere down there is water that is of the temperature that the bait likes, so why don't we just use that? The good news is we can - we just have to reach a ways down there to get it.
When looking at a few of our water temperature measurements, we can see the contrasts in the temperatures across a depth profile from early June to late August - not only does the upper layer of water warm, but the lower depths also warm well into the 60's by late summer.
This new deep-water pump rig consists of a Rule 2000 gph bilge pump and two sections of 1-1/4" pool vacuum hose, and assorted fittings and wire. You could also use a 1100 or 1500 gph pump - each have 1-1/8" fittings which would work with the build procedure described below - you'll just have slow tank fill/drain times (though you should see considerable improvement over the use of 5/8" garden hose).
The hose is joined with a 1-1/4" x 1-14" male bard to male barb fitting that can be found in the plumbing section of your local home improvements store. With the hoses I used, the barb fittings were tight enough that hose clamps are not needed, though over time they may be.
Earlier in the article I mentioned cutting down one 26' foot section of hose into a 14' and 12' section. This gives me some options to configure the pump with a hose that is 14', 26', 40' or 52', as needed. However, I need an easy way to extend or shorten the wire to match the length of the hose. I ran across a source for some watertight Delphi connectors that are of suitable wire gauge & amperage, and they even have them pre-assembled in a harness so that I do not have to acquire the proper crimping tool. I like the Deutsch connectors better, but given these are available pre-assembled, they will do. I plan to order a few sets and install female and male end on each section of hose so that I can connect/disconnect the various lengths of hose as needed, allowing me to have the right length of hose through the different times of year, without having to manage the bulk of the full length on the boat year-round.