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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.


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?


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.


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??


Great, thanks for the advice. I’ll look in to that.


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.



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?



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


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?


Hi, what do you think about this kind of solution?

Seem very elegant and space saving.. but is enough for dissipate the heat produced by k40?

Thank you for your awesome work!

Jenny Searcy

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?


any things to avoid or to look for in dish soap? or does it really not matter?


can i use any car coolant for my cooling system


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


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.

Fred Heim

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.


what surfactants and biocides
any suggestions? where to buy? ratios needed?


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…


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



Do you think that EC6 non-conductive coolant would be ok to use with R/O Water or would i be better using distilled {all my R/O is free/also it will be running thru
Cheers Phil


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


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!


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.


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.

Luis Martín

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.

Luis Martín

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.


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.