HYDRO Rapid ph fluctuations

[Tersky]

I've been having an issue where one of my plants in my hydro setup has rapid drops in ph. Here are the specs of my grow:

2ft x 4ft x 5ft Apollo grow tent
250w HPS
GH Flora trio and Calimagic
RO Water

My setup is small at the moment. I have two 2 gallon buckets with net bucket tops, one 4 outlet air pump with two hoses and air stones going to the buckets. The current plants are actually left over seeds, probably 2-3 years old, just stored in baggies in a sunglasses case. This has been a problem grow from the beginning but thats a long story lol. My plants are now 2 weeks into flower (Blue og and 1024) and when i test ph (twice daily) one of the res's ph has dropped to 4. It happens occasionally on both but one more consistently than the other. This includes right after fresh res changes! I have some theories based on some things i've researched, one being the temps of my res. I measured them and they tend to be around 70-74 deg F. A second was that i just started using RO water, but i'm pretty sure once you put nutes in the water the ppm goes up and a drop from 5.5 -6 to 4 in less than 12 hrs is still extreme. A third was that i have some kind of pathogen. Maybe i need to replace all my hydroton, tubing, airstones and even air pump. I clean them all between grows but i have never changed them out and it's been a few years. The plants are not going to be very productive, but mistakes were made and the seeds were old so im not worried about that. Other than being stunted they are healthy, no deficiencies, algae, bugs ect. Roots are healthy, but the size of the root system is a lot smaller than a healthy plant would be on both plants, but like i said, the seeds were old. Anyone have any insight and recommendations on this issue?

[YYCannabis]

How are you testing your pH? (Pen or reagent?)

I would suggest some type of pH buffering agent, but I don’t know enough about hydro growing to say if the buffering agent is safe. Maybe go back to using whatever water source you used before you started to use RO water to see if the pH dives stop.

Cheers
YYC

[RagWeedDWC]

I'm at a loss on why the PH fluctuates that much, I would start with a change out of fresh hydroton regardless. Is your nutrients the type that "Auto" adjust PH? Somewhere there was a chart that pointed out the ph change to temperature, it does not support that amount of change for temperature only. Are the reservoirs clean? It could be something still growing on the sides causing it to crash. I'm still fighting keeping it stable in my own, but have not had that extreme of a drop.

[Tersky]

Yes i clean everything with h2o2 and/or bleach (light solution) and rinse thoroughly. I really think it has to do with res temp and dissolved oxygen. Either that or some pathogen is hiding somewhere where i cant find it.

[RFheavy]

Whats your ppm at when you change res?

[Tersky]

well that depends on what conversion you use. my tds meter says 877 pm but im not sure which conversion it uses. ec is about 1.7 m but it doesnt matter what the ppm is the ph still drops, Just did a res change, guess ill just have to do alot of ph correcting until harvest then i can start replacing my setup

[Tersky]

Well...the past two res checks have been pretty normal. It figures...I've been struggling with this for at least a month, probably closer to a month and a half. Im going to try tap water next time but idk, maybe i messed up preparing the nutes or something for a while. I really cant think of anything i did differently this time tho.

[YYCannabis]

Do you let the bulb on your pH pen get dry between uses? I was having wonky readings for the first few dips whenever my bulb dried out. I just swab it with a wet cotton swab and it returns to normal.

[Tersky]

I use the drops. I just got a ph pen but am still waiting for the storage solution so i havent used it yet.

[YYCannabis]

Hopefully your water-goblin is gone.

[smoorman]

I keep my ph and ppm pens submerged in shot glasses in an inch or so of water all the time. Seems to work and always matches calibration solution. I noticed you said ppm at 877 and EC at 1.7. Foxfarm feeding schedule uses a ppm/700 EC conversion. Yours appears to be based on a 500 conversion. I'm not sure why there are 2 different conversions. I've had the same ph plummeting issues and always seemed to solve it by staying on top of ppm and ph.

[Tersky]

Oh. I have come up with a solution. So i use RO water, which ph can rapidly fluctuate. My tap water isn't exactly hard at 175ppm, but something in it makes it hard to change the ph in it. Like 10 drops of ph down to bring it down 2 tenths (0.2). RO water, one drop can bring it down 1 full point (1.0)....Soooo i do 3/4 a gallon of RO to 1/4 a gallon of tap water and this allows me to have a stable base for my nutes. I now adjust and top off every couple days and res change 2x a week (late flower and 2 gallon buckets) but have not had any issues of ph drop since. I let the tap water sit for 24-48 hrs to evaporate the chlorine. I think it was because RO water has nothing to buffer any changes in my res ph and it just went wonky.

[YYCannabis]

If your water had chlorine in it, you can reduce the time to just a few hours by adding a bubbler to the bucket. Or anything that continually disrupts the waters surface.

Some areas use a chemical similar to chlorine in the water, but it never off-gasses no matter what you do to it.