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You can go to Lowe's or Home Depot and buy a fish pond pump that will replace the one in your cooling tank if it dies on you. They only cost about $50 - $60 as compared to the $200 you mention, John. And they will last, theoretically, forever if you keep the water clean.

Another thing: Don't put so much antifreeze in the water. At first, we used the recommended amount of 1 gal. of antifreeze to 4 gal. of water. We cut that down to 1:5 or even less. Just enough to make the water turn green. Not only is antifreeze expensive, but it can cause the pumps to die prematurely if there's too much. (Buying "epoxy sealed" as opposed to "oil filled" pumps also helps them last longer.) When we cut down the antifreeze ratio, we found that our pumps virtually quit dying on us. Where before, we would end up replacing pumps every six months or so. Now we replace, maybe, one or two a year.

I have found that, IF you change the water often, you don't need to use distilled water, either. Just draw a big bucket full of tap water and let it sit out for a week or two so the clorine can dissipate. The antifreeze should take care of any hard water scale, etc. Just remember to change the water and flush out the lines at LEAST a couple of times a year.

Don't forget that the $200 price included a tank, lid and connecting hoses. For replacement, we buy those "Little Giant" NK2 pumps. They are oil-filled; do you have a model number of the epoxy sealed ones? I'd like to try them.

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I bet you can find one you like between $50 & $70.
I use different submersible pumps (from them) for coolant and water circulation around the shop.

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut http://www.muellersatomics.com/

I cut the old cords off the original tanks. (Save them if you can! You never know when you could need a line cord like that!) We never used the switches on top of those (Blue and white Strong) circulators anyway. They were plugged into the convenience outlet on the side of the projector. The power was turned off when you shut the projector off at night. There is a hole in the top of the lid of the tank. I just pop out the plug and run the cord out that hole. Everything else should be "plug-and-play" if you bought the right pump. If the unit is in a high traffic area, or you are otherwise worried about spillage, just make a new plug to seal the hole around the cord.

Whether you put less antifreeze in the tank or not is up to your discression. Like I said, it can get expensive. At the temperatures and pressures we're using it for, the "thermal properties" of antifreeze only gives you a little bit of benefit. The way I understand it is that the main reason to use it is for its antibacterial/corrosion inhibiting properties. (It keeps the water from getting scummy.) If you clean the tanks out and back-flush the lines often enough you shouldn't have a problem with that anyway.

One thing... discarding used antifreeze.
As you know, antifreeze it quite poisonous. Don't dump it down the storm drains, etc. If you can, you should take it to the local recycling center for reclaimation. If you can't do that, it's okay to dump SMALL amounts of it down the toilet. (Unless your local regulations prohibit it.) Your average municipal sewage plants can handle this kind of waste as long as there isn't too much of it. If you have a large multiplex you probably do this kind of maintainence in stages. One or two tanks full of antifreeze down the toilet, every couple of weeks, until the whole place is done won't hurt anything. All of your rinse water should go down the toilet as well.

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Non-poisonous antifreeze:
Regular antifreeze is especially dangerous because cats and dogs (and some kids) think it tastes good. They'll stand there and lap up a puddle of antifreeze until they get sick and die. IF you get the animal to the vet fast enough, there IS an antidote. Once the antifreeze gets into their liver, it is metabolized into toxins that cause all kinds of systemic damage, for which there is no cure. If you know your pet has been into the antifreeze get it to the vet, pronto! If I remember right, you only have about 20-30 minutes, depending on the size of the animal and how much it drank. After that, It's "Goodbye, Old Yeller!"
Non-poisonous antifreeze has two things going for it. 1) It doesn't tase good, so kittys (and kiddies) won't try to drink it. 2) Although it WILL make them sick, it won't kill them. It is STILL poisonous. It's just not AS poisonous.
Thing is, it's a lot more expensive. When you have a 10-screen to keep running, that can add up. If you change the coolant 2-3 times per year like we do, the difference really adds up!

The reason for distilled water - it reduces electrochemical corrosion by reducing the conductivity of the water. There can be quite a nasty mix of dissimilar metals in a cooling circuit - copper is one of the nastiest. The water should be replaced regularly because it gets contaminated.