RO water and buffering

[H20gro]

Ok, chemistry came along in high school about the same time as cannabis for me. So i chose the more hands on, experimental branch of the science, ie, smoked weed and didnt pay attention in class so please help me understand how to get ro water “stable”, especially regarding ph.

Ive been told to mix it with tap water and/or to use both ph up and ph down (buffer?).

As it is now, my dwc plant in week 8 of flower seems to have water ph dropping unless i add tap or ph up…. Even then it seems to slowly drop. Ideally it would rise as nutes are used i thought.

Anyway, help understanding this and ideas to approach ph “stability” w ro water would be greatly appreciated.

I am new to ro water and still learning..

Tia

@bluter @Delps8 @Bill284 @OGpapa

 

[BAKIND]

You shouldn't try to set ro water at a certain ph. Instead you should adjust to your target ph after you added your nutrients to your ro water. If you are cultivating in DWC then you will be adjusting your ph frequently because the plant is changing it by feeding and drinking from your mix. If you are going to grow with dwc, I would recommend rdwc. You should be able to keep your ph more stable.

 

[bluter]

don't mix RO and tap. recipe for crap.


just like @BAKIND described. start with RO, add nutes, then ph. RO stays extremely stable while you feed after you ph. don't worry about it after feeding, the ph at the time you feed is the only important ph there is.

 

[OGpapa]

Might be helpful. I'm a soil guy. There are lots with better information. But here is a guide I would find handy

 

[H20gro]

Im noticing that w straight ro, after i add nutes the ph is right at 6. Should i bot “buffer” w anything? Despite the gradual drops in ph?

Thanks again

 

[H20gro]

Yeah i got this on the other thread and have been referring to it. Seems my ph ahould be rising as ppms/ec decrease, so maybe i just need a stronger solution? Keeping it around 700/1.4 now. Remember it is recovering from nute lock before the ro

 

[bluter]

Im noticing that w straight ro, after i add nutes the ph is right at 6. Should i bot “buffer” w anything? Despite the gradual drops in ph?

oops forgot you were dwc. you do need to monitor ph in dwc for the reasons outlined in the chart. ph to 5.8 every time when you swap out the res. monitor and adjust between.

edit : you should be tracking your ec as well between.

 

[H20gro]

You shouldn't try to set ro water at a certain ph. Instead you should adjust to your target ph after you added your nutrients to your ro water. If you are cultivating in DWC then you will be adjusting your ph frequently because the plant is changing it by feeding and drinking from your mix. If you are going to grow with dwc, I would recommend rdwc. You should be able to keep your ph more stable.

Thank you for the info. I actually just purchased all i need for rdwc and next month i will be starting a skywalker og grow w it. Guess fluctuating ph is just part of dwc. Thank you again

 

[bluter]

how often are you swapping out the res ? you should be completely changing it out every few days in dwc. little less in rdwc.

 

[bluter]

Yeah i got this on the other thread and have been referring to it. Seems my ph ahould be rising as ppms/ec decrease, so maybe i just need a stronger solution? Keeping it around 700/1.4 now. Remember it is recovering from nute lock before the ro

what's it doing now ? that'll inform you to the next move.

 

[H20gro]

how often are you swapping out the res ? you should be completely changing it out every few days in dwc. little less in rdwc.

Actual res swap only happened after the nute lockout. Since then ive used ro water and flushed every 5-7 days. Because im scrogging, the res swap is a headache.

 

[H20gro]

what's it doing now ? that'll inform you to the next move.

I just flushed this morning. Added 700 ppm solution w no ph up or down as it was at 6 after nutes added.

Its now at 5.8 and 690 ppm. Water used daily (about 2-3 quarts).

 

[H20gro]

Her

 

[bluter]

Actual res swap only happened after the nute lockout. Since then ive used ro water and flushed every 5-7 days. Because im scrogging, the res swap is a headache.

what do you mean by a flush ? if you can't swap a res how can you flush ?

pic says you're hungry for sure and potassium deficient.


edit : what scale are you measuring ppm on - 500 or 700 ? as a quick guess i'd wager you need to be up about 800 or so. you can run dwc / rdwc thin with great results. in passive i'd be near 1100 or so at the same development. 1200 or higher gets dicey.

 

[Delps8]

Re. pH of RO water - good info here.

Re. swapping a res every N days - as I posted in a thread here on 420 a couple of years ago, I'm not convinced that a grower should swap a res simply because the earth has circled the sun a given number of times. "Swap it every seven days" may be convenient but…maybe not.

I haven't updated that thread with what I've learned over the past couple of years but the only fact-based discussion I've seen is in these two sources. If you search for "Nutrient Management in Recirculating Hydroponic Culture" you'll be able to download the PDF. Bugbee is the lead on that and I found a lot of good info in it. The other source is this site, more specifically "Nutrient Solution Management and Longevity".

Given that you're working with a small amount of nutrient solution, you might see pH and EC change pretty quickly so it's wise to stay on top of pH and EC.

 

[H20gro]

By flush, i mean i use a liquid transfer pump to remove the water… pour in fresh water while pump runs… put about 10 gallons through it, then i add nuteient solution to res


Since the lockout it has definitely had deficiencies. Ive had it in ICU since then and been very attentive

I cannot answer which scale. Im using a digital meter that ive calibrated twice this week. But unsure of 500/700.

Im not at 800 ppm or higher bc ive been gently increasing nutes since lockout. Also, that chart led me to try and hit between 500 and 700 ppm (1-1.4 ec) based on ph/ppm/h2o levels and their activity.

I was wondering aloud earlier if i should increase nutes concentration to affect ph dropping.

@bluter

 

[Delps8]

don't mix RO and tap. recipe for crap.

That's a recipe for diluted crap.

By flush, i mean i use a liquid transfer pump to remove the water… pour in fresh water while pump runs… put about 10 gallons through it, then i add nuteient solution to res

No need to do that. The amount of chemicals that remains on the roots when a bucket is empty is "measurable but insignificant". Just emptying out the bucket and adding new nutes will get the job done.

My res holds 28 gallons of nutes and I end up replacing about 26 gallons. There's some water in the rootball and maybe an inch of water than I can't pump out but the gallon or so that's left behind doesn't make a difference.

Since the lockout it has definitely had deficiencies. Ive had it in ICU since then and been very attentive

I cannot answer which scale. Im using a digital meter that ive calibrated twice this week. But unsure of 500/700.

Im not at 800 ppm or higher bc ive been gently increasing nutes since lockout. Also, that chart led me to try and hit between 500 and 700 ppm (1-1.4 ec) based on ph/ppm/h2o levels and their activity.

If you're in the US, your meter is probably set to convert EC to PPM on the 500 scale. To remove all doubt, switch to EC or dig into "the docs" for the EC meter. I ran smack dab into this in my first grow (2017) and it was not a pretty sight.

When I post TDS values, I use "xxx/500" to indicate the scale.

I was wondering aloud earlier if i should increase nutes concentration to affect ph dropping.

No.

The goal of giving fertilizer is to provide the chemicals needed for a plant to have "sufficient" levels of chemicals. That's it. The sufficiency range is quite broad and fertlizers are designed to provide the plants with what they need.

Dropping pH indicates either a problem in the root zone or it indicates that the plants are taking up the chemicals in the nutrients which result in pH dropping. Falling pH can be caused by root rot and has other symptoms including brown slime on the roots and a very distinctive, foul odor.

When I do a new res, pH always drops for a couple of days. It's simply how the plants are taking up the different chemicals in the ferts.

 

[bluter]

By flush, i mean i use a liquid transfer pump to remove the water… pour in fresh water while pump runs… put about 10 gallons through it, then i add nuteient solution to res


Since the lockout it has definitely had deficiencies. Ive had it in ICU since then and been very attentive

I cannot answer which scale. Im using a digital meter that ive calibrated twice this week. But unsure of 500/700.

Im not at 800 ppm or higher bc ive been gently increasing nutes since lockout. Also, that chart led me to try and hit between 500 and 700 ppm (1-1.4 ec) based on ph/ppm/h2o levels and their activity.

I was wondering aloud earlier if i should increase nutes concentration to affect ph dropping.

700 ppm at 1.4 ec would be 500 scale.

some of the leaf fade would be expected but it is kinda wanting and does have a potassium ask.


edit : i'd go another 50 to 100 ppm higher and see. it's feeding immediately.

That's a recipe for diluted crap.

lol. hard to both hit like and laugh on the forum.

 

[H20gro]

700 ppm at 1.4 ec would be 500 scale.

some of the leaf fade would be expected but it is kinda wanting and does have a potassium ask.


edit : i'd go another 50 to 100 ppm higher and see. it's feeding immediately.




lol. hard to both hit like and laugh on the forum.

Adding 50-100 ppm, do u believe it should be potassium heavy, ie, GH bloom heavy? Or more equal amounts to add up to 50-100?

 

[Delps8]

Adding 50-100 ppm, do u believe it should be potassium heavy, ie, GH bloom heavy? Or more equal amounts to add up to 50-100?

Bluter will give you more cogent advice soon, let's hope. Until then, the screenshot here shows the amounts of chemicals that are some of the GH products. If you scan across the line for "K", you'll see how many PPM of K are in a given fert. Not a lot, eh? Adding even 50PPM worth of K could cause a serious imbalance, AKA "lockout".

One warning - I don't think there's any evidence that "bloom nutes" actually do anything for cannabis. You might check out this thread for a perspective on that. Full disclosure - I've drunk the Koolaid. I uses dry ferts, same mixture from seed to chop.