This is my 5th grow, 1st time in DWC. I’m using two 5 gallon buckets with 6-inch baskets of clay pebbles growing a Lemon Cherry Gelato and an Apple Fritter. I have about 3 gallons of solution in each bucket. I use Jacks 321 nutrients, silica, and hydroguard.
I’m 7 weeks into flower and (I think) the plants look great. Nice dense buds, very frosty with trichomes, no discoloration on leaves. (see pics below)
But I’ve noticed a dropping pH in the last week or so. Once a week, I change the reservoir with fresh solution using RO water, silica at 1mL/gallon, Jacks 321 (I’ve adjusted the Jacks 321 levels to give me an EC of 2.3-2.4). I then aerate the new solution for 1 hour before adding phUp to get pH to 5.8, I then add hydroguard at 2 mL/gallon and swap out the buckets with the fresh solution.
After 24 hours I’ve seen pH drop to 4.8-5.2. I then add either RO or more Jacks 321 (depending if EC is higher or lower than 2.4) and ph Up to bring the pH back to 5.7-5.8 range.
Then the following day, pH is down again.
The roots look good, kind of an off white/cream color, not slimy, and don’t smell bad.
Reservoir temp is 68-70 degrees, tent temp is 69(night)-77(day) degrees, tent humidity is 58(day)-65(night)%
Dropping pH is fairly normal at this stage of the grow, just use a few drops of pH up or silica to correct.
Also at this stage, their nutrient needs are reducing, thus if you need to top it up, just use pH corrected water or if doing a change out reduce the nutrient strength.
Also of note is the cause of the pH dropping, which is caused by the nutrients that the plant is not using being still in solution, which indicates they need less nutrients.
I do chilled dwc. I would take the ph up a little higher so that by the time i check it, later on, its not as low as youre getting. I maintain my ph between 5.8-6.2, change out solution 7-14 days. I start with 3 gallons, and adjust ec daily by only adding water when needed.
The above info is all good and should be considered.
Based on your reports I would suspect the reason you’re seeing this is a few things working in tandem. Your roots are off gassing Hydrogen as they are taking positively charged minerals and must maintain electrical balance. The more roots release positively charged hydrogen the more acidic your solution will get. This is called cation exchange and has been happening the duration of your grow.
The reason you’re seeing it be more prevalent now is likely due to having a larger root mass and less solution. Your potassium silicate and pH up (probably also potassium silicate or a blend of) work to buffer your solution the other way. Early in grow your solution fills more of the res volume and has more buffering capabilities. The smaller root mass releases less positively charged hydrogen and the regular res changes are enough to hold ph more steady with less adjustments. As you get later in grow the ratio of solution to root mass changes and there’s no longer enough solution to hold off the increased amount of hydrogen from the larger root mass.
The fact that you’ve had a relatively smooth grow to this point, your plants look solid, and roots look good, this is almost a textbook scenario of a cation exchange issue. The easiest way to fix this is to increase the volume of your res. Maybe not easy to do at this point, but may be easier than adjusting ph daily.
Realistically, 5 gallon buckets are a much better option for recirculating systems that has an additional res and plumbing to hold more solution. Running straight dwc you’d be better off with a 20+ gallon storage tote. If you’re pressed for room even a 12-15 gallon tote would be significant upgrade.
Morning, Chester….. in the way that I grow deepwater culture, this pH drop in heavy flower is what always happens, and it’s normal. As long as you can see the nutrient value is decreasing and your roots look good and the plant looks good you should be good, I sometimes have a pH of 4 for four days before I do my change out, which I do every seven days. I have noticed that some plants are more prone to drive the pH and others don’t move the pH very much…. Just what I’ve experienced in my single tote grows
Great information above and yep, normal
I’ve been able to capitalize on color with lower ph in DWC as well. Of course, genetics are the biggest factor but when you couple pink & purple genes with cool temps & low ph… wow!
Ur grow looks awesome and ur in line for some fire smoke!
Thanks for all the replies! It’s good to know I’m not doing anything obviously wrong and it’s normal to see dropping ph. I’ll keep monitoring it and adjusting ph daily.
One more question… I just noticed some brown spots on a few of the leaves. Not much. Spots on 2-3 leaves total on each plant. See pics below. Could this be due to the low pH? Or do I have some other deficiency?
During the length of my grows I always have one or two leaves that show some kind of issue, but I look at it as just a pimple. It’s not really an issue if the rest of the plant is looking good….. I do see some tip burn and a little bit of clawing. not sure how much nitrogen you’re given right now, but they don’t need much in flower….
I was about to say you’re pretty close to harvest so your flower is about at Max. So it’s needs are going to drop. I would keep on doing what you’re doing for about another week to 7 days and get ready to break out the hangers. But I might end up early harvesting too. These are just my thoughts and I am not a professional
