Calibrating TDS meter with distilled water?

I have read, and heard in the videos I watched, you shouldn’t calibrate a TDS meter using plain distilled water. Something about the 0 ppm messing it up or not giving you a true reading?
Although I have heard it suggested many times, that it is ok to do so. Plus, I will be buying it anyway, to mix with my pH packets to calibrate that. So if I have it on hand anyway, I’m wondering if it’s OK to calibrate my TDS meter with it?

No, you rinse in distilled water. My Apera came with 1,413 (NaCl) solution, although mine measures EC.


Beware, not all distilled water is the same. There was a major comparison done 2 years ago by the battery industry and believe it or not, the very best (purest) distilled water is WalMart brand…go figure.


No, you absolutely should not use distilled or otherwise zero EC/PPM water like demineralized or deionized water to try and calibrate your meter.

The way these meters work is by measuring electrical conductivity (EC), and water without anything in it can not conduct electricity. And to calibrate to a “scale” you need a “base point” to calibrate it to, like a NaCl(sodium chloride, aka salt) solution.

Something like this:

You also do not want to mix a TDS solution with a pH solution when calibrating either a EC/TDS/PPM meter or a pH meter, these are different things and most pH mixes will increase the amount of dissolved mineral salts which would throw off a EC/TDS meter. Also, a TDS solution could change the pH.



@Myfriendis410 @MacGyverStoner @Hogmaster @Majiktoker @bob31 @Donaldj @garrigan65 @Countryboyjvd1971
Ok I tagged everyone I could think of, so my apologies if this is not in your area of expertise…
I finally got my meters today! I went to my local Hydro store and picked up GH 7.0 ph solution and GH TDS calibration solution.
I think I can handle the ph calibration, but the TDS has me a bit confused…
The solution I got says:
1500 ppm - NaCl scale
2190 ppm - 442 scale
2930 S - microSiemens
but after looking online it says my TDS-3 meter is calibrated at 342 ppm NaCl scale?
So what should I be reading with this solution on my TDS meter? When I calibrate it, what should it be reading?
Im going to check my tap water (will it be different from my kitchen faucet compared to my outside faucet?) and my tap water after I leave it out for 24 hours with some occasional stirring (to let chlorine and stuff come out, no bubbles yet, dont have air pump/stone until I decide what medium Im going with).
Is there anything else I should do?

Edit: Adding a question… whats the best way for me to store these pens? Should I rinse them in filtered water, shake them out, and cap em? Or should they be sitting uncapped in solution or filtered water or something?

NaCl scale is the important part. NaCl is sodium chloride, also known as plain salt or table salt, and this is the main salt in the ocean.

So use this one, and make sure your meter reads 1500 when you dip it in this solution.



Hope this helps


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Any advice on storage?

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Doesn’t the meter come with storage directions @xDeeTeRx

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Probably not, unless you have a household water filter system that filters water for your kitchen faucet.

This will allow chlorine to evaporate out of the water. However not all chlorine treatments are made of chlorine gas. If they are chlorine salts, they won’t evaporate or be removed except by filtration, like a R/O system with a deionizing filter.

I wouldn’t worry about the chlorine too much, it is actually a needed nutrient in small amounts for the plants.

As far as chlorine evaporating from the water, this won’t change PPM.

The TDS probes should be rinsed in pure water, demineralized, deionized, R/O, or distilled. Then just put the cap on.

The pH probe is made of a super thin glass membrane, be very careful with it as you don’t want to crack it.

You can also rinse it off with purified water. You can buy pH storage solution, or you can use the GH 7.0 ph solution.

You only need put a couple drops on the “sponge” near the glass pH “orb”, or the sponge in the cap, or on the orb itself before putting on the cap. The white fiber like thing sticking out near the glass orb is the “sponge” unless you have only the obvious sponge that is in some pH meter’s cap.

The TDS probes don’t matter if they dry out completely as long as they have been well cleaned.

But the glass orb on the pH probe should never totally dry. Most of the time, just a few drops of the purified water is enough. But you do want to use the pH storage solution, or GH 7.0 ph solution – for long term storage, or relatively often as to keep the “solution” inside the glass membrane steady.



Kind of - its a cheap meter so its a combo of japanese/roughly translated english - just says rinse in filtered/distilled water and dry (from what I understand of it) but I was sure something I read says you shouldnt let it dry out? I just wanna be sure Im extending its life as long as possible

I have a cheap blue one. I rinse it put the cap on it and put it back in it’s place. Some meters have different requirements but I would go with those directions.


So I can just test it out of the faucet? (no filter system) and whatever reading I get is the same reading I’ll get in 24 hours?

Why do people leave the water out w air stones running for 24 hrs sometimes before they use it? Is there anything beneficial with leaving it out like that? It wont change the ppm, will it change the ph or something maybe?

There is the potential of too much chlorine. So getting rid of some it could be beneficial. Also, highly aerated water has more dissolved oxygen, O2, in it, and this is good for seeds and roots. Plus too much chlorine could kill beneficial organisms in organic soils.

Yes, a fresh out of the tap glass of water should test PPM the same pretty much as one left out for 24 hours.

It might change the pH. Aerating too much CO2 into water can make it more acidic, as well as some other gasses from the air can change pH slightly, but it shouldn’t be much of a worry.



The airstone creates bubbles which speed the gassing off of chlorine by increasing surface area in laymen terms


Ok I’ll be posting my readings later tonight after I put the boy to sleep! Exciting!
Hoping my tap water is usable!

Hi Mac nice to see you kicking around


If I end up running 2 DIY DWC buckets like I had originally planned - I’ll have to get an air pump and stones to do that - just to get rid of some chlorine
Do you think its necessary? How will I know if I have chlorine that I can bubble out or if doing that is making any significant difference?

I don’t bother with that step usually I just leave water out overnight but when in a rush I occasionally do I also favour rainwater to tap water :wink: My plants love it and ppm is super low ph is almost nuetral
I favour rainwater over my RO water too I only tend to use RO for starting but it greatly depends how your ladies react to your tap water


Check with your water supplier. They should be able to give you a water report that will tell you what is in your water, good minerals and bad, as well as what type of chlorine they use in the water they supply you with.

Once you test your water’s PPM, you will have a better idea if you can use it relatively trouble fee in a DWC. But it is not the chlorine that is the biggest problem in most instances, it is more “hard water” which is usually made up of a lot of calcium carbonates and calcium bicarbonates, these if too high can raise pH and make it troublesome to keep your pH from climbing above optimal levels. 5.8pH is optimal for DWC, and no higher than 6.1 and no lower than 5.5 to avoid pH related deficiencies, toxicities or lockouts. A PPM higher than about 150 PPM/0.3EC ms/cm might be problematic.


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