PH dropping from 6 to 5.5 in less than 12 hrs

[Dinger]

Here is my thread describing what I am doing: Dinger’s Hydro Green Crack Grow Journal 2019

Doing a NFT with grodan cubes and a grodan slab. I am in my 5th week of flower and I have a 4 gallon reservoir that is changed out with the 3 part GH Flora Nutes and 4ml of calmag once a week. Everyday I replace about a gallon of tap water that has 1ml of calmag mixed in to get the PH up to 6.0.

12 hours later the ph has already dropped to 5.5, so i add more water. If I cant get the PH up with just water due to space limitations then I use a small bit of PH up.

Is this normal? My buddy said don't worry about it and not to chase the PH, just keep adding water and change the nutes weekly. This is my second grow with the first one done in coco coir, so I am still a bit overzealous.

Thoughts?

 

[bobrown14]

Root exudate is the cause of the pH drop most likely.

I grow in soil but I've read a lot of how soil-less grows work.
I think your buddy gave you good advice. Its better to have lowerish pH than higher is my thought.

 

[Dinger]

Root exudate is the cause of the pH drop most likely.

I grow in soil but I've read a lot of how soil-less grows work.
I think your buddy gave you good advice. Its better to have lowerish pH than higher is my thought.

Thanks for responding!

Time to google. Got no idea what that means.

 

[10gal]

Thanks for responding!

Time to google. Got no idea what that means.

5.8-5.8 is were u want your ph in rockwool

 

[bobrown14]

Root exudate is what the roots put out to feed organisms that in turn feed the plant.

The exudate changes the pH of the soil local to the roots - in soil-less that exudate mixes with the medium and has the ability to lower or raise the pH based on what the plant wants from the medium. It could change the pH either way.

So you can see that influence when you test. 10gal suggested that 5.5 - 5.8pH is your sweet spot.

 

[Dusted]

Make sure your pH meter is calibrated. That sounds like way too much pH swing for tap water plus cal/mag

 

[Dinger]

Make sure your pH meter is calibrated. That sounds like way too much pH swing for tap water plus cal/mag

I picked up another meter and it reads pretty close to the same.

somebody else mentioned it might be environmental like I have some kind of pathogen in my reservoir. They said two to three teaspoons of hydrogen peroxide per gallon should help clear that up.

I have no experience with the 3% hydrogen peroxide does that sound right to anybody?

 

[labexperiment]

Yes it sounds right, but its been 4 or 5 years since I co-grew a hydroponic set up. Hopefully another member with a better memory or more experience chimes in.

 

[Dusted]

In the last week I too have replaced my pH pen and see what you are seeing. I guess the sensitivity of my old pen, which finally died was shot. I purposely add a bacterial/fungal spore innoculant to my system to control organics build up so there will be some organic acid production, but that should be rapidly degraded by the bugs. I was a water chemist for years so I understand this stuff.

For years I have consistently added acid (75% H3PO4) to maintain 5.8 in my hard (180 mg/L hardness) high pH (7.6-7.8) tap water system. I did change nutrient suppliers a couple of grows ago and just discovered that instead of straight calcium magnesium nitrate, my new suppler uses about 10% of their N as ammonium salts. As ammonia is removed from the system the pH drops. I also discovered today that the new nutrients buffer out to the correct pH without acid addition. I don’t want to deal with pH up since it is a pain with hard water and precipitation of calcium and magnesium out of solution. Same with silicate solutions

Now that I have a new pH pen (2 point calibration) and no acid addition I have reduced my reservoir size from 60 to 40 litres and will have to replace the nutrient solution when the pH gets too low. Instead of weekly it may have to be every 3 to 4 days, as required.

 

[West Hippie]

I’ve questioned this before, I grow flood&drain with a 20 gallon reservoir. I used the ph perfect nutrients and it would start out between 5.45 and 5.6 which they say 5.6 is there sweet spot . I would watch it rise in 7 to 10 days to 5.9-6.0 then I’d change the reservoir with fresh ph perfect nutrients . It took a dive on me and kept falling below the 5.5 and grandpa Tokin caught it acid rain (was running CO2) and gave me this chart and I still use it today !

 

[Dusted]

Interesting chart. My ec and pH drop fairly quickly after changing out the nutrients. pH starts at 6.2. Next day it is 5.5. The day after it is 5.0. It stabilizes at 4.5 eventually except for the daily swing I get by adding the high pH tap water. I also go through large amounts of water every day. I have to top up about 10% of my reservoir volume daily, but with hard pH 7.6 tap water. I figure I was growing in pH 3.5-4 nutrients for the last two grows when I was adding acid. They turned out pretty good. I just gave up worrying about it in the last week or so.

 

[West Hippie]

Interesting chart. My ec and pH drop fairly quickly after changing out the nutrients. pH starts at 6.2. Next day it is 5.5. The day after it is 5.0. It stabilizes at 4.5 eventually except for the daily swing I get by adding the high pH tap water. I also go through large amounts of water every day. I have to top up about 10% of my reservoir volume daily, but with hard pH 7.6 tap water. I figure I was growing in pH 3.5-4 nutrients for the last two grows when I was adding acid. They turned out pretty good. I just gave up worrying about it in the last week or so.

My tap water has a ph of 8. 3 and the ph did just what yours is doing went back to ro water . When I run it through the ro system I get 7.2-7.3 ph . Got away from the ph Perfect nutrients. Worked good but was costly.
MegaCrop nutrients now and I have control of the ph. I have a mother plant in dwc of the widow, pretty chopped up just took 10 clones off her , I started the ph at 5.6 and in four days it has risen to 5.89 . I couldn’t ask for any better results according to the chart , ph had a rise , water falling , and the ec falling !

 

[Dusted]

I attribute it to the ammonium salts in the N blend I now use. For 20 yrs I made my own N base solution from calcium nitrate. I could also buy the K/P solution with micronutrients. Not anymore. Using straight nitrate I had to add acid. With the ammonium salts in the blend the pH drops during use it seems

Live and learn