Question on Water supply / comment on measuring PH

New here and new to all of this. I bought an Atwater kit to give this a go with one seed. Seed is close to going in and I am setting up water. ~ 4gallon.
Question is do you use tap or distilled water in such a small setup? I ask because of PH. My tap water shows really high based on my reagent that came with the kit. I bought a dip tester as well and it is about 6.5 (sending it back).
So bucket water was about 6.5 on dip tester and off the chart on reagent. I was going to do a calibration on it, so before I setup test bowls I decided to just test distilled water. And they were both measuring the same! This is why I am sending this tester back. I can handle calibration but not that level of inconsistency. I know they arent very accurate but never expected that.

You were spot on about inaccuracy. A quality pH meter is one of those crucial parts of the grow. BlueLab and Apera make great ones. Anywhere from about $60-$200 on Amazon.

As far as your kit, I’m not familiar with it. I grow in soil/Coco. When using tap water, you do want it to sit open for 24 hours, before using, to dechlorinate. Sorry I don’t have much else for ya. Others will chime in soon, no doubt


Believe it or not my tap PH is anywhere from 6.5 - 7 with a blue labs pen. Really the chlorine is what you dont want. It kills any benifical bacteria you may be looking at useing, aside from that you want the iron, calcium, and magnesium in the water. I use cheap $20 camper water filters that i screw onto my hose, that removes chlorine, but also removes the iron, calcium, and magnesium so i have to pre-ppm the water with cal-mag extra.

Defietly want good tools, you can only be as good as what you have to work with, good PH, and EC meter are crucial if you want to build any sort of correlation between numbers and your observations of your growing plants. This helps to measure so you dont repeat mistakes, and do repeat wins as you expirement and make tweaks and changes.

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As mentioned tap water needs to set to let the chlorine evaporate.
Chlorine is acidic, so once its gone the pH rises. Mine goes from 7 to 8,5 after setting 24hrs.
That same thing happens in your soil unless you let it gas off.
Some places use chloramine, a different version of chlorine and it does not go away ever. You have to filter it out or buy special chemicals to eliminate it. Look for those in pool supply stores or areas of Lowes or Home Depot.
You should be able to look up your water test by searching "water report “YOUR CITY, STATE”


I spent two decades working in private and public aquaria, I’m pretty well versed in water chemistry.

Straight chlorine is never used, too unstable and corrosive.

Most municipalities use chloramine NH2Cl instead of chlorine (typically in the form of Sodium hypochlorite NaClO). Chlorine is unstable and very corrosive (sodium Hypochlorite is pretty much bleach). Chloramine is a molecule of Chlorine and Ammonia that stabilize the free electrons in the chlorine atoms and prevent it from evaporating quickly in the water supply and being corrosive.

There are many methods to break this bond and neutralize both elements. Some aquarium water treatments will break the bond and neutralize the chlorine leaving the ammonia to be consumed by the aquariums biological filtration.

RO will purge both but RO water can be very raw and have limited buffering capabilities. PH adjustment is for naught if your water does not have the ability to buffer/stabilize at a desired PH. Waters ability to buffer and maintain PH is one of the most overlooked aspects of indoor gardening and aquarium husbandry.

I use an aquarium product and then filter with a gravity filter I made with activated carbon and ion exchange resins. This keeps the waters buffering ability intact and makes adjusting and maintaining proper PH easy while neutralizing and removing the chlorine and ammonia atoms/molecules.

I would also recommend mixing all water 24 hours before use to ensure there will be no ph fluctuations. I’ve seen too many times water without an ability to buffer drop or rise drastically within 24 hours of it being adjusted. That rise or drop will continue in the growing medium and sometimes be even more severe.


Distilled or R/O water, or any water source with a TDS under 100 ppm cannot be reliably tested by using EC (electrical conductivity). Says so right in the Bluelab instructions.

If doing hydro most use R/O so they have complete control over everything in the water.

I lived in a municipality where the TDS of tap water was 550 ppm. If running any nutrients you have to factor the initial TDS into your total. For example: target 900 ppm with that water you’d be adding only 400 ppm of nutes with an unknown quantity of suspended solids in the tap. This would be unacceptable for most hydro growers. Or coco or Promix for that matter.


My tap water pH is a fairly constant 7.8 (the EPA allowable range is 6.5 to 8.5). I burn through a lot of pH Down for my irrigation water to lower the pH to 5.8 for my coco soil. Over the next 3 days, the pH will drift back up to about 6.5.

With distilled water, carbon dioxide in the air will dissolve into it, creating carbonic acid in the water. This can lower the distilled water pH to 5.8.

Im sure everyone has a favorite ph pen and a reason why. Heres mine i use hm digital ph 80. Its easy to use easy to clead is relatively cheap at 60 bucks and i bought a bottle of 7 ph solution for 15 bucke that lasts about 6 months and only need the one solution to calibrate.

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@samiam It is best to use distilled or RO water in your hydro setup mostly because it is a clean slate to start making your nutrients. Another factor is the minerals in unfiltered water can accumulate in your system causing issues.
But I have seen growers use tap water and be successful with hydro, I personally use distilled or water thru the ZERO water filter.
My current favorite pen is made by VIVOSUN and measures Temperature, PH, PPM and uS and has held up the longest of any I have purchased in the past.
Good luck!

My first one started measuring wrong for some reason or another, but my wife ordered the Apera ph60. I’m not sure how often I actually neeeeeed to calibrate it, but I do every two weeks.

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Mine acted silly when the batteries were low.

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My tap is about the same, 7.7-.8. When using Jack’s A&B with epsom, at 4/2/1 (grams), it put my pH at 6.3-.4 consistently. In coco I had to pH it 5.8-6.0. I use citric acid crystals, though. Cheap and takes very little. But, If I used dehumidifier water, I could add 2ml silica per gallon, then mix Jack’s, and I landed at exactly 6.00. I’m doing a couple autos in FFOF now, then when the soil depletes, using Jack’s. And starting a totally organic grow soon. So hopefully very little pH’ing the next few months.

Mine started to read .1 off, then .2. I changed batteries, cleaned best I could and was still calibrating every few days, and eventually having to somewhat guess til the new one came in.

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Thanks. Interesting since someone earlier mentioned distilled was not optimal. Guess it shows many opinions and ideas right? Reason I am here! I have a Vivosun as well that I got on amazon. It has the yellow PH meter and the same you mention on the blue one for EC/TDS.

for my current situation - Atwater Hydro. tap water has been in it running 2 days, coco rock in basket and rinsed off.
Today PH is 3.5 (added ph down yesterday butt guess it was too much), EC us/cm is 2642 and PPM is 1286. While PH is low, the other two readings seem high right? Looked at conversion charts and those numbers were not even on it. I did add about a 1/4 teaspoon of nutrient yesterday Mendocino 30-10-10. Maybe should have waited on that.

thoughts on those numbers? Once again, no plants are in it yet.

My Apera ph 20 is also .1 off did you ever get it to properly calibrate to 7.0? I left it in the calibration solution for 3 or 4 minutes and it finally came down to 7.0. I even ordered new solution. I just ranwith the 7.1 keeping it arround 6.5 to 6.8 i figured it was within reasonable numbers.

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I did. But when it started going off by .2, I didn’t want to mess anything up because my tap isn’t always at 7.7. and I was going back and forth with that and dehumidifier water. My wife ordered the ph60 before anything and it’s been solid since.

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@samiam not sure why someone would say distilled is not optimal…it is a clean water that you can customize to your needs. I had the 2 pen Vivosun but I was constantly calibrating the PH one, my current Vivosun is the all in one pen version and seems to hold the PH calibration better.

If you have not put your plants in yet and have the time start over and take notes as to what you are doing so you can go back and review to make changes if needed for your future grows. Use this as a trial run learning how to use your system. Start slow with nutrients a number like 1286ppm for seedlings is way high even if we consider your tap started at 300ppm. My starting ppm is around 200ppm.

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The pen below is the one I’ve been using for quite a while. I calibrate it every new grow but it stays pretty consistent. I like the fact that the company is well known and they sell replacement probes in the event of an accident

The PH pen bulbs need to stay wet or that will toss them off if you dont store them properly. I like the blue labs pens because you can replace the PH probe if you need to and not buy another new meter. Same for a guardian if you can afford it. Never had issues and use these to validate each others accuracy. Calibrate every 3 weeks.

Storage cap for probe.

Thanks, re-reading I think his comments were on using a PH pen and its ability to measure distilled water. My apologies. Not sure why this number is so high. I tested my tap water and it was closely inline with what you mentioned. Guess I will dump this and start over.
thanks again

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