Calibrate PPM Meter With Tap Water?

I have a question, so here it goes... I know with all hydroponic water testing meters there is a calibration solution to use to calibrate the meters. Now say I calibrate a PPM (TDS Meter) with the proper solution and it is reading out perfect. Now say my normal tap water from the faucet reads 250ppm. Would it be possible to calibrate the meter to 0 using the tap water, therefore when I test the nutrient solution in my reservoir, the ppm reading would be ONLY be reading the total ppm for nutrients only and not the nutrients ppm + the ppm of the tap water? It just seems that this would be easier than subtracting the ppm of the tap water every time you take a reservoir reading? Am I on to something here? Or would this not work?

Why are you subtracting the ppm of the tap water?

I subtract the ppm of the tap water from the ppm read out to find the true ppm of the nutrient solution. So say you want to feed your plants @ 1200ppm and your tap water is 250 ppm.. The reading of the ppm meter will say 1450. But since we know the tap water ppm is 250 already, you would just subtract the tap water ppm from the 1450ppm, and this will tell you that you have 1200ppm of nutrient solution. But if you could calibrate the ppm meter to the tap water to 0ppm, then I was thinking that when you take a reading from the nutrient reservoir, the reading would be 1200ppm and would show just the ppm of the nutrients? Correct me if I'm wrong, I've just been curious if this would work and haven't seen the question come up really in the forum

AlphaPhase said:

I subtract the ppm of the tap water from the ppm read out to find the true ppm of the nutrient solution. So say you want to feed your plants @ 1200ppm and your tap water is 250 ppm.. The reading of the ppm meter will say 1450. But since we know the tap water ppm is 250 already, you would just subtract the tap water ppm from the 1450ppm, and this will tell you that you have 1200ppm of nutrient solution. But if you could calibrate the ppm meter to the tap water to 0ppm, then I was thinking that when you take a reading from the nutrient reservoir, the reading would be 1200ppm and would show just the ppm of the nutrients? Correct me if I'm wrong, I've just been curious if this would work and haven't seen the question come up really in the forum

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That 250 isnt just nothing..it contributes to the overall "strength" of your nutrient solution.

You shouldn't subtract the ppm of the tap water. You're not (in your example) feeding at 1200ppm, you're feeding at 1450ppm. High ppm in the tap water means you have to use less nutrients. That's why people with "dirty" tap water buy RO filters or buy bottled water. The "true" ppm of the nutrient solution includes whatever is already in the water and whatever you add to it.

I'm guessing it will read incorrectly.. guessing it will read higher tds than whats actually in the mix and I don't count my base tap water as my nutrients either

The ppm of your tap water can change depending on time of year and what your city is adding to it..... So subtracting 250 as a general rule will not always be accurate.

This is some awesome info. I am kind of mind blown about hearing that I should not subtract the tap water ppm, I was always under the impression to subtract it, now I know. I've been growing for quite some time but there's always something to learn everyday.

Can anyone explain a little better why not to subtract the ppm of the water? I know plain tap water already has stuff in it, that's why the ppm has a reading, but what in it affects the nutrients? Ie: if using RO water that has a ppm of 0, how come you can add say 700ppm of nutes for veg? But if the tap water has a ppm of 250, you should only add 450ppm of nutes? Does adding less nutes to tap water somehow end up equaling the proper ppm for the nutes? I've never had too many problems with subtracting the ppm of the water from the total ppm, but then again I always taper my nutes up until I feel the plants are feeding full force.

Sorry, I'm rambling, but I am very interested in this because I have never used RO water, though I want to try a grow with it eventually.. But I swear someone told me to subtract ppm of water when adding nutes, but it's been a longgggg time so I'm not sure if I just made that up in my head or something lol.

Everyone feel free to chime in.. Experiences with tap water vs. RO water.. Any positive negative effects noticed? What about growing without subtracting the ppm of water compared to a grow where you did subtract the tap water ppm?

Thanks every1

And st0wandgrow, youre right on, I didn't even think about the ppm fluctuations of my tap water over the course of the year. That answers my original question, now i'm on to a whole other tangent lol

your tap is probably mostly cal/mag and if you add your tap ppm + your nute ppm to = your total ppm you will be under feeding. that's the reason you don't add cal/mag to your tap water really unless you use an RO system. RO systems I believe just help give your plants a more direct uptake to your nutrients due to the water being pure of everything that it needs. Most likely your tap has stuff your plant doesn't even need as much. if your tap is 250 and you want 1000ppm than your total ppm should be 1250.

^^^ this isnt true.
When you use RO water with 0 ppm that leaves more room for NPK + micros.
That 250 you're starting with is calcium, magnesium, copper, chlorine etc.
Your city or county or whatever should have an online water quality report.
Mine looks like this.

You all have a valid point, it's kind of conflicting information though, I'm starting to think that RO vs tap water really should be based on how much nutrients is in the tap water to begin with, some tap water may be just right and other cities tap water may not be so good and RO should be used. I think my tap water is ok, I just check out the county water quality report, thanks tightpockt for pointing that out. There is some Cal and Mag in my tap water already, along with a whole list of other stuff, but the levels of the stuff in the report aren't too bad at all. I'm still scratching my head wondering if i should just go with what the ppm meter reads including the ppm of the water, or subtract, I guess it's all how the plant responds. I'll start with the using the total number as a whole ppm and I can always work my way up little by little and see how it affects the plants. I'm starting a new grow journal using a ebb and grow system. Follow along if you want and see how it goes, hopefully it goes well First time using ebb and grow, but I'm a verteran using hydroponics in general so i'm pretty excited to try the new system out. Here's the link to my grow journal.

https://www.rollitup.org/t/prop-215-rdwc-round-one.829129/#post-10508722

Thanks again for all the info & if anyone wants to add any more info I would like to hear it, the more knowledge the better. Thanks again

Your right when you say your getting conflicting answers lol. Most people do not count the base when adding nutes but some do. I really dont follow any charts or even the actual numbers really. My base is 250 and I run at around 650-700 ppm's when plants are established I watch the changes and add or subtract depending on plant, and the fluctuation in levels, as well as what PH is doing. I keep notes on each strain I do so know in advance where to start. I'm a newb so Im sure my way is not always the proper way lol.

you need to do a conversion to get accurate ppm that are available to your plants.

Brimck is right! If you need to know actual nute levels you need to subtract base

@waterdawg - to each his own, if it works for you theres no need to change your method

@brimck - For sure, I always like to know how much I'm adding of just the nutrients minus the base of water, it gives me a little better idea of how much micro/bloom etc. I've added. I wish I had my own water testing kit that told me exactly how much mag and cal is in my tap water though.

AlphaPhase said:

Or would this not work?

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It will not do what you are thinking it will do. You should only calibrate to a known solution designed for the pen. Get yourself a couple different gallons of bottled and purified water at the store. Also fill a gallon jug with your tap water. Add the same amount of nutrients to each gallon. Test again. That will help you see what's going on in there.

"@waterdawg - to each his own, if it works for you theres no need to change your method"
Actually you said you were going to do what I do, I dont subtract base and it is part of my total amount I guess lol. I just try and keep it around the 650ish mark which is perhaps a bit low for some. If I actually didnt use the base I would be at 450ish. Lol now Im confused!

i'm confused to lmao, 450 does sound low, but as tightpockt said "That 250 isnt just nothing..it contributes to the overall "strength" of your nutrient solution." which makes sense, but also would leave the nutrient solution a little low. My advice would be to start low and add nutes until the perfect amount is being used for happy plants, and then see what the total ppm is, subtract the 250ppm after the max nute dose is reached, and see how much nute ppm is in there just for peace of mind. a total 650 ppm (including the water ppm) might be perfect for certain strains (at only 450ppm nute strength.) But some plants might be able to take a 1250ppm during veg (1000ppm nute strength) with no negative effects. Also, some ppm meters are different, some have an EC conversion of .5 and some have an EC conversion of .7, and that also makes a huge difference of what the ppm meter is reading, because one persons meter may read 500ppm, and someone elses meter may read 700ppm, in the same exact reservoir

Using RO water would also make a huge difference since the ppm of RO water is very low, so the ppm reading is mostly the nutes that have been added, as stated somewhere above on this thread. I've never used RO, but using it does seem to have it's benefits, but also very low amounts of clorine from tap water also has benefits in my system to keep algea and such at bay