HYDRO Sudden pH drop

[Tokin]

Did a reservoir change (last one before flipping into flower). Using 65% recommended amount of nutes with 100% recommended amount of CalMag and R.O. water. The pH was stable at 6.2 - 6.3 (optimal for CalMag absorption). Four days later the pH started dropping quickly, down to 5.2 in less than 24 hours. I added a gallon of tap water to try to buffer until I could flip her into flower. Less than 24 hours later it is down to 4.7. I am defoliating and flipping today. The plant looks wonderful. ( I am in the process of moving some photos over to this computer so I can post). Has anyone seen the pH change rapidly as a result of total consumption of CalMag? The TDS is reasonably stable (within 30 - 40, lower with water usage ). I am growing a 100% sativa photo-period.

My set-up is:
2' x 3' cabinet
KIND XL450 LED
20 gallon reservoir
LOTUS nutrients
Two circulation fans
Two speed variable exhaust fans
Oxydator ozone generator in reservoir
Exhale CO2 bag

[RagWeedDWC]

I have seen this happen with a root issue and although I have not grown anything but autos in a couple of years, I do recall prior to flipping, the plants feeding extremely heavy which will cause a drop.

I would flush it for at least 24 hours, let it catch its breath and easy into the flowering mix for nutrients.
By all means please post pictures.

I have used this chart in the past, it is pretty good, right on the money but gives you a good ideal.

[Jebidiah]

I stopped adjusting my pH until it was in the tote agitating I know it goes in at 5.2 but I typically have to lower it 10 minutes later. When I add water between nutrient changes the pH will tend to hold but it too sometimes creeps up. Now about 4 times through the life of 1 plant I will have the pH drop and around transition it usually dips the hardest also it will go up in flower and be hard to get back down at least once. I blamed my well water and started checking it everyday and keeping it in range, just falls in line with my ocd.

[Tokin]

Thanks RW. The roots are massive and white. It does look like a massive feeding frenzy. I saw something similar near harvest time with a Super Silver Haze Auto. Naturally I couldn't solve the issue since I harvested after the flush. I will flush before adding flower nutes. I was wondering if the sudden drop could be related to a specific element.

[Tokin]

Thanks Jebidiah. I also don't adjust pH for 24 hours after a res change. I installed a recirculating pump in the res to mix the nutes more quickly ( I also use it to drain the res ). It takes about an hour to mix but it still takes a while for the pH to stabilize. After the dip/spike did you see it remain stable?

[Jebidiah]

Yeah it’s like the plant just wants to make sure you are paying attention. I read somewhere and can’t find it now that a plant will go through changes and cause pH changes…how credible that is I have no clue but it set my mind at ease moving forward.

[Tokin]

Here is a photo of the six week old veg.