What to cool a laser machine with has been and probably will be a split opinion for many users.
When asked in forums and discussion groups the replies are many and spread across a lot of different mixes and products.

With this article i will explain the different mixes, what they do and how they fit our machines, and why some may not fit.
In the end, it´s up to you as the owner to decide what mixture you want to use, read this article to decide and see what properties the different mixtures have and what the goal is with your machine.


Preventing growth of bacteria, algea and other microorganisms. You do not want algae in your laser tube, it prevents heat transfer and may kill your tube.
I have seen usage of small amounts of bleach or chlorine in the coolant, it acts like a biocide too but in wrong amounts it will make the coolant very low pH and the mixture is corrosive for metal parts in the loop.
Biocides made for hot tubs or pools shouldn’t be used either.
There is readily products for this so i would suggest using a real biocide. Check out PC water cooling stores.


Or wetting agents is a premix, like Water Wetter, Purple Ice, HydrX and Hy-Per Lube with many more names depending where in the world you are.
Note 2018-01-20: Since i wrote this article it seems like Water Wetter has changed their contents or it differs between EU and US markets, so i would wait with adding water wetter at the moment until this is confirmed. It has showned higher conductivity than earlier.
Wetting agents lowers the natural surface tension of water. The effect causing water beads to form.
This helps water transfer, prevents bubbles from forming, lowers the viscosity and acts as a corrosion agent for metal parts in the loop.
Dish soap is one type of surfactant, but it also contains alot of other additives, like perfume and similar, read the bottle before using.
In auto stores you can find additives for your wiper fluid, DO NOT use this in your coolant, most of them are flammable and is dangerous to add to a 16000 volt system, just don´t do it to be safe!


Our laser tubes have ~16000 volts flowing trough the tube, the water inside the machine will get charged if it contains any particles carrying this charge.
Distilled water has almost no particles at all and do not get static charges. When you add anything to the water, you amp up the static charges also.
Why is this bad for a laser tube?
First off, having a couple of thousand volts in our coolant tank is dangerous, it hurts pretty bad if you happen to touch it.
Second, if alot of the energy in the tube goes away to charge the water, less energy is carried to the other end of the tube, thus lowering the power of your laser tube.
Third, static charges helps mineral build ups in your tube. With time these may create hot spots and a temperature difference in the tube, cracking it.
Remember, without any minerals/particles in the tube, you cannot have a static charge.
The static charge may also interfere with the beam, making it deviate from the path and hit the edges of the end mirror and you get a split beam inside your machine.

Cleaning and maintenance

Basic rules for your cooling tank
– Keep it out of sunlight
– Keep the return hose below water surface
– Have a lid on the tank, leave a small gap around the hose for pressure differences.

When changing the water in your tank, use 50-50 mix with Listerine+distilled water, or vinegear to flush your loop for a hour.
Then refill with your favorite mix of coolant.

Using tap-water for shorter runs

It works to use tap water for shorter runs. Use with caution, fill your tank with tap water, use the machine and empty the tank right after use. Add a mixture of vinegear+water or listerine+water and run the pump for 30-60mins.
I would not suggest keeping tap water in the tank longer than 3-4 days.
Depending on your tap water quality, it may go bad over night, or you´ll be fine for two weeks. Just as a precaution i never recommend tap water at all, even though i use it myself sometimes.

Different coolant mixtures, and their properties


Tap water

+Good thermal properties
-Microorganisms will flourish
-Very high conductivity
-Risk with mineral deposits creating hot spots, depending on water quality.
-No corrosion inhibitants

Distilled water
+Good thermal properties
-With time, microorganisms may flourish
-No corrosion inhibitants

Distilled water + RV antifreeze
+Fair thermal properties
+Corrosion resistance
+Good protection against algea and other growth
-False sense of security using a pre-mix.
-Higher viscosity, less thermal pickup
-Higher conductivity (about 400x more than distilled)

Distilled water + surfactants + biocides
+Excellent thermal properties
+Corrosion resistance
+Not conductive, less than 2μS/cm (tap water: 1000-2000μS/cm)
+Good protection against algea and other growth

Distilled water + surfactants
+Excellent thermal properties
+Corrosion resistance
-With time, microorganisms may flourish

+Good thermal properties, similar/identical to Distilled water
-Will re-ionize very quick and go back to regular water.
-With time, microorganisms may flourish

The “I have done it, you are wrong”-tale

Of course there is users who have cooled their laser with tap water, RV-antifreeze, camel urine or whatever, just because it works for them isn´t a rule to say it works for everyone 🙂
How fast a laser cooled with camel urine will fail depends on so much more than the coolant, as power usage, how often and how long it´s used, room temperatures, lasing temps of the water and so on.
The facts are there, you be the judge of how you want to cool your machine, i can only suggest what to do, or not to do.

We are currently rewriting this article – check back later.


50 thoughts on “Watercooling, different coolants”

  1. Starting with my K40 laser, what’s the best way to keep your water as fresh as possible, I have a 30l tank, I’m going to order distilled water,I know you can get algae (happened to my friends lasertube), how often is it best to change your water.

    1. Keep it out of the sun, this will slow down algea alot, keep a lid on the tank and have the return-hose below water level to keep it fresh longer.
      How often depends how you take care of it, as said above. I change water every 6 months when i can measure a increase conductivity in the water.

  2. Just starting with my new k40. Thank you for your fantastic website!
    I started with pure distilled water and millions microbubbles was forming along the laser tube. I was almost adding some dish soap when I saw the dishwasher rinse aid (Finish) on the kitchen cabinet. I added some (~10ml on 10 l) and after 30 seconds all the microbubbles were diapered. I saw the microbubbles moving to the end of the tube, forming a bigger bauble and after going out of the tube in one time.
    The rise aid help the water to slide away from the dishes so they can dry faster, so maybe it is a good solution for the laser tube.
    What do you thing about?

    1. The additive in dish soap, “Finish” you mention and some detergents contains “surfactants”, this is whats lower the surface tension in the water and get rid of all bubbles. I stay away from mentioning any brands though because they can be different between countries. Some additives found in computer water cooling can also be added for the same effect. And the tablets for dishwasher machines can also be used dissolved in water first before put in the loop with similar effects.
      If it works, use it! 🙂

      1. Thank you for your reply.
        As I wrote, the product I used is a rinse aid and not dish soap. For the dishwashers there are three things to use: the granulate salt, the detergent tablet and the liquid rinse aid.
        A small part of rinse aid is automatically released only in the end, after that the detergent is already washed away and is for have super dry and super shine dishes and glasses. Now will look like I want promote this product :)! Hahaha.

        1. I actually bought some yesterday. I tested it with a meter (EC meter) to see if it was conductive, it was very low and that´s great for our use. Not tested it in the laser coolant loop yet though 🙂

  3. Hi, just bought a k40 and readying it for its first run (thank you for all the tips btw!). I’ve read the scare stories everywhere regarding using anything but distilled water will cause a black hole etc, so to be on the safe side I’m going to take the advice. Distilled water is a little expensive in the UK so I thought I of just using the water from my heat pump dryer. Great theory but is it acceptable in practice do you think??

    1. I know some users are doing it, i wuoldn´t. Even if its coming from a dehumidifier, pump dryer or similar where it takes water to steam and collect it again there is a big risk that it contains a lot of crap, some machines are better than others on filtering the crap out but as a general rule i never recommend it.
      Check for battery water, it´s often cheaper and pretty much the same thing as distilled.

      If you have a EC/TDS-meter (measuring conductivity in fluids) you can test the water from your dryer to see how conductive it is. You can find one on ebay and similar for cheap. They are not 100% accurate but good enough for what we use it for.

        1. Also in the UK, also just ordered a K40, and finding distilled water locally seems impossible so it looks like it’s going to be online only, so delivery charges don’t help.

          I tried local chemists and all they seem to offer now is deionised water, had one chemist say it’s the same thing which did make me doubt him a bit.

          Ordered a home brew fermenting bin to use as the water reservoir.

          1. Try to find battery water, it´s often distilled (check label). Distilled vs deionised is similar in water quality but they act different in our setups. It will work with deionised too but not as long.
            With my first laser i made my own distilled, a big pan on the stove with tap water and a funnel upside down on the top with a hose to a closed 25L home brewing bin, took some time but it worked pretty good 🙂

  4. Hello,

    I recently found your site, great info !! I built myself a cooling box out of some peltiers I had. Think of like a mini freezer / powered ice chest you take in the car.

    The problem Im having is that if Im not doing alot of cutting i.e the tube isnt getting hot then the water and biocide in my cooling loop starts to get icy. Im terrified that will ice up to the point that flow would stop.

    Do you know of an antifreeze that meets all your other suggestions?


    1. Check ebay, amazon or aliexpress for a W1209, its a relay with temp-sensor. So you can set a min-temp when it turns off the peltiers. I have the same thing on my peltiers, it turns off at 15c, above that its on.

    2. Wow, COMPLETELY missed the RV antifreeze in the list. that solves my question lol Disregard

  5. I forgot another question 😛 for a “classic” system with a bucket, what is the minimum water quantity ? I’m running out of space… so I need to find the smallest solution.. as example 10 liters of water in a bucket sized for 15 liters is enough for running the laser for 1 hour of (more or less) continuous work?

    1. Depends on your room temp and how much power you use. You can go with 10L and a couple of ice jugs in that to keep it cold for longer time.

    1. It works partially, a radiator can only pull down the temperature to ambient temps. But a small one like that will have trouble disappating the heat quickly enough. If you have a bigger one you might get water temp close to your room temp. Or if you put it outside the window in the winter you get free cooling.

  6. I’m new to k40, arrives in 1 week. Re the coolant water, I see the best (all green +) is Distilled + biocide, + surfactant. What is a good biocide to use (? Vinegar) and how much? And surfactant, how much, a few drops, more?

    1. Bleach is a good biocide, 15ml per 10L of water is a good start. A few drops of dish soap works as surfactant, add a few drops and run the pump 15min, and look inside the tank, when the water stops curling up on the wall the tension is gone. Add 4-5 more if needed.

        1. When i used it, i bought eco-friendly stuff, with less perfumes and oils. Probably doesn´t matter much 🙂

    1. No, most of them are conductive and will field charge the water from the tube, causing both less power output aswell as lowered gas regeneration affecting life length of the tube.

  7. Hi i have a 60w laser tube, as a cooling system i have two radiators with fans and a water pump, the temperature of the water gets to high like 30 C°, because it’s a hot enviroment , what kind of coolant do you recomend, it’s possible to use any car coolant

    1. The radiators can´t cool down the water any more than ambient temperature. So if you have 30c in the room the rads will never cool below that. You need active cooling, either a CW5200 or dump some jugs of ice in the water tank to keep it low. Keep away from car coolant.

  8. Considering use of EC6 Mentioned before. Would it be best to use by itself or to add something to it? Also, what amount makes the most sense? I’m considering creating a loop with a radiator somewhere in the mix that would hold about a gallon of liquid overall. Is this too much or too little? Currently sing stock setup with a gallon of distilled water and the provided pump, but my readout tends to hover between 30C and 35C (room temp shows as ~22C before I even start the machine up.

    1. 25% distilled to that wont hurt if you want to save some dollars, but you can go 100% EC6 too.

  9. Thoughts on this coolant: Antifrogen Sol Ht
    Propylene glycol base super low corrosion on most metals. I picked up some for a solar heat application.

    1. Looks like really low conductivity and good density for our lasers, try it.

    1. Surfactant can be a few drops of dish soap until the surface tension is gone, or stuff made for PC water cooling is another option. For biocide a tbl spoon of bleach can be used in 10L of distilled water, not in metal loops though as its corrosive.

      1. Hi there I’m thinking of using EC6 coolant in distilled water for my machine… How much would you recommend I put into say 10L of water???? Great blog by the way…

        1. One 1L bottle would give you pretty basic protection, for best use 100% should be EC6 as its a premix, not a concentrate. But i have used PC cooling before with good results. Also make sure to keep the tank out of sun light, and as air tight you possible can.

  10. Hi. Very interesting topic. Looking around how to cool my K40 laser and what to use. What is your opinion about EC6 non-conductive coolant? The supplier claims that their product has Electrical Conductivity <2µS/cm at 24C. It's not cheap, but if it is suitable, maybe it is good investment? They claim it should last for 2 years.
    There are specs from them:


    • Pre-mixed with No Need for Additional Additives – Ships ready for use
    • Corrosion protection for Copper, Brass, Steel, Nickel and Aluminium Proven to ASTM D3306 and BS6580 standards
    • Prevents build up of Algae & growth within in your liquid cooled system
    • Electrical Conductivity <2µS/cm at 24C * (most competitors struggle to reach <10µS/cm)
    • Non-Toxic and RoHS Compliant
    • Freezing Point – 6C
    • 85% Bio-degradable Within 30 Days
    • Available in a None coloured option or an expanding range of *non toxic UV colours
    • Shelf Stable UV Reactive Dyes of up to 2 years
    • EC6 is a true Eco Friendly Product


    1. That one looks like a perfect coolant, if you have a closed system where air from the room cannot contaminate the coolant. The actual problem with distilled is not the water, it´s the shit falling down into the coolant.
      Similar coolant to the one you list above is the kind made for welders, they have similar standards.

        1. RO is worse, it has a tendency to “re-ionize” from the air and go back to “normal” water quicker than distilled will. It may also rob any metal from the ions in the loop corroding them. How much and how quick depends on a lot of features, but i would go with distilled instead.

          1. The RO “re-ionizing” quicker than distilled water is a myth. The water does not care what process was used to remove the ions in the first place.

            RO water with <10µS/cm versus distilled with <10µS/cm is basically the same. RO is just cheaper.

            Source: MSc in Chemical Engineering

          2. Thank you for the info, we contacted a professor at the university who have helped us writing a new post about this matter and fixing some other details. Greatly appreciated comment!

  11. I have built several custom PC rigs and I am researching cooling for a K40 I plan to buy. I have seen very little info on using mineral oil (zero conductivity) and heat sinks/fans for tube cooling. If you could provide any information on why not to use mineral oil that would be great. I know it is a bit more expensive than water but as far as use of length it can not be beat. I am not very familiar with laser properties and how it would react to mineral oil. Thanks!

    1. Mineral oil are denser and will cause problems inside the laser tube. The flow needed for it to work properly will endanger the glass tube due to the force applied. I have tested regular mineral oil without problems, but the gain is very slim. And cooling the oil through a heat exchanger or radiator will not work for most users, as the cooling will be limited to ambient temp, and that is often too high for the health of the laser tube. A laser tube wants 15-18c temperatures. Maybe if there is a oil with lower viscosity it can work, but with that there is probably a loss on the thermal pickup/exchange instead.

  12. Hi again,

    Why not use Destilled water and some antifreeze over tap water? Seems like better combo over tap water even if it costs some fe NOK.

    1. There is so many different antifreeze brand and blends out there, and many of them contain additives that will create problem in the laser tube. Either by making the water too conductive so the water is field charged (output power and gas regeneration process lowered), and some will act on the hoses, so it´s easier to just stay away from them. If you find one with low conductivity and not eroding the hoses, you can use it 🙂

  13. Why do you say “keep the return hose below water surface”? I like to hear the water trickling and so don’t do this at the moment.

    Thanks for the website and all the useful info.

    1. The trickling water creates air bubbles in the tank, get a visual indicator or a flow sensor that breaks the connection for the machine to use the laser if the flow stops 🙂

    2. Porque sino cada vez que se pare la bomba, se vaciará el tubo de agua y se tiene que volver a llenar en el siguiente trabajo, teniendo siempre más riesgo de que queden burbujas de aire en el interior del tubo.

      1. Because but each time the pump stops, the water tube will be emptied and it has to be refilled in the next job, always having a greater risk of air bubbles inside the tube.

  14. Well, here’s the “I have done it, you are wrong” comment.

    Over 6 years and 5 lasers (3 x k40’s) I’ve only ever used tap water. I toss a cup of bleach in there to stop algae and then forget about it.

    My brother who lives in a colder area adds anti-freeze, I don’t need that.

    The oldest functioning tube (not killed by me being dumb) I have in a K40 is 3 years old, it works fine (down on power but that’s expected considering its age). Water flow rate hasn’t slowed.

    Now I wouldn’t advise using hard well water, but if your local city water is low mineral, then use it.

    When first started I read all the scare stories, including the bollocks “it’ll corrode your mirrors!” one. As usual no-one can produce a tube that’s been ruined by running plain tap water through it. By the time any minerals have built up to cause a problem the tube will have died of old age.

    If distilled water is cheap where you are then use it, note that it can rust metals more than plain water will (fittings and the stainless steel tank in your chiller). De-ioned water can be more damaging to metals.

    My main problem was the plastic tubing going brittle. Get black stuff, UV doesn’t attack it.

    1. Thanks for sharing! I use tap water too now and then, but i keep from suggesting it as water is very different even down the road. And we have seen very high conductive water acting on the power output aswell as the regeneration process. In my summer home i can use the tap water directly from the spring, but in the city it´s so bad the PSU starts to coil whine 🙂

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