A Question About pH.

Here's the deal, I have 12 plants, 6 of one strain 6 of another. I am using ProMix BX with 25-30% added perlite. I mix all my nutes in a giant tub then give each plant 1 gallon. So they all are potted in the same medium and all get the same amount of nutes at the same pH. Today I watered with plain R/O water and tested the individual run off pH of all the plants. The pH ranged from 5.9-6.7 and everywhere in between. Why do all the plants in the same conditions have different run off pH?

pure RO water is very unstable. It has no buffers at all in it to keep the ph stable. So it varies wildly like that.

Is there some kind of fix. How can I do a feed-water-feed-water schedule if the water is going to send the pH all over the place?

You can add a little sodium bicarbonate (baking soda) to the water. It acts as a buffer and will help control the wild ph swings. I have done this for other plants and it works well. I still use it all the time on the water I put in my planted aquariums. Never tried it on MJ though. I usually just use a mix of about 25-30% tap water and 70-75% RO water for plants now, that will buffer the water a bit. Sometimes I just use straight tap water.

baking soda is ph up, never heard it called a buffer. put some in water and retest the water. also a strong ph up lil goes a long way.

I know lot's of people use R.O. water so surely I can't be the only one having this problem. What do the rest of you guys do? I have R.O. water for a reason, it wouldn't be good for me to mix it with my well water.

Thanks Kerovan, +Rep for the help.

Stoner Smurf said:

I know lot's of people use R.O. water so surely I can't be the only one having this problem. What do the rest of you guys do? I have R.O. water for a reason, it wouldn't be good for me to mix it with my well water.

Thanks Kerovan, +Rep for the help.

Click to expand...

RO water has a VERY low ppm bro like around 20 ppm or less.....that means R/O water is Magnsium and Calcium diffecent.... Meaning you NEED MORE OF IT!! tap water has a HIGH ppm like around 250 ppm or even higher so thats plenty of Mg and Ca its actually TOO MUCH so what you want is a happy meduim say around 125 ppm to 150 ppm so thats why people mix 75% R/O water with 25% tap so they can raise there ppm and get some Mg and Ca in there water.......Now if you DONT want to mix tap water all you have to do is go get some Mg and Ca supplments... "Botanicare" has a great Ca and Mg supplement that comes mixed togeather in one bottle. go get it and a TDS meter and add the Mg and Ca supplement to your R/O water tell your PPM reaches 125 -150 then add your nutrieants and other additives....Make sense??


Rember that the lower the PPM the more sensitive the water is to PH change

I already use Ca/Mg+, actually I use Botanicare Ca/Mg+. I use Ca/Mg+ when I feed the ladies their other nutrients. My plants get a well balanced mixture of nutrients every other water. I alternate between feed, plain RO water, feed, etc. So you're suggesting that I use Ca/Mg+ In every water including the plain RO water as well as the feedings?

Stoner Smurf said:

I already use Ca/Mg+, actually I use Botanicare Ca/Mg+. I use Ca/Mg+ when I feed the ladies their other nutrients. My plants get a well balanced mixture of nutrients every other water. I alternate between feed, plain RO water, feed, etc. So you're suggesting that I use Ca/Mg+ In every water including the plain RO water as well as the feedings?

Click to expand...

Hmm thats a good questions ... i use Nutes on ever watering so ive never run into that that situation... But id use the Mg/Ca on every watering wether theres nutes or not just so its easyer to Ph your water and keep it from floating so much. Plus the only reason Not to add would be because your already getting too much of it from tap water iand since your adding your own Mg Ca to R/O water you can make sure you dont put too much in. so just put enough in to get to 125 - 150 and it should be fine I have two grows one i use just straight tap water and thats does me good with like 250 ppm so if that dont over do it then im sure your Botanicare Mg ca on every use will be just fine if you keep it at or below 150 ppm

Also you said you use the Mg Ca already... so what does your ppm look like straight out the R/O ? and how high do you let the ppm go before you start adding your nutes and Ph?

My PPM meter broke, but assuming nothing has changed in the last month the PPM of my straight RO water is 38. I've been doing all my feeding off my notes because I know x amount of nutes equals y PPM from previous feedings and stellar notes that I've taken. I know I really do need to buy a new PPM meter. So when I feed nutes the PPM is 1350ish and the next water which is plain RO has a ppm of 38.

Stoner Smurf said:

Is there some kind of fix. How can I do a feed-water-feed-water schedule if the water is going to send the pH all over the place?

Click to expand...

The ph of runoff water is actually a very poor indicator of the mediums ph. The only accurate way to tell is to test the medium itself. If the plants look healthy I would not worry about it.

They don't all look healthy actually. I noticed about 5 min ago 2 of the ladies with low ph run-off have Mg deficiencies. One of each strain. Both girls had pH run-off of 5.9.

I dont use reso system to water i water by hand to waste so i dont check my PPM after i put the nutes in i check it first then Ph then add nutes then check Ph so im not sure if 1350 ppm is good have to ask someone else thats more of a hydro guy i use a passive hydro to waste....But ya i would take your 38ppm R/o water and get it up a lil on the times you only use water and no nutes ....thats just me though.....

PPMs are much more telling when dealing with runoff measurements. Run 3 gallons of 25ppm water through a 2 gallon pot and runoff reads 300. You may have a salt buildup issue. A nice base too start from.

You have to test the PH of your water and nutrient mix every time before watering/feeding. The ideal PH range is 6.5-6.8 for soil, if its not that you need to use forms of PH up or down to bring the solution to that specific PH range. At that PH range your plants will be able to absorb all nutrients properly, when it slips out of that range it starts to lock out certain ones such as Mg. and Cal. (the first to go most of the time). In order to be an efficient grower you will need to start check/testing/maintaining the proper PH. Like they said Baking soda is good PH up but only use a very very very small amount at a time it will bring the PH up very fast. White distilled vinegar is good for PH down but dont go using it to adjust after you put too much baking soda in that can cause lockouts and what not on its own.