Rapid PH Drop in DWC

My grow:
1 Northern Lights / 1 mystery seed
4 weeks into veg (pants are about 12", lots of growth)
2 bubble buckets, plenty of air, RO water (0 ppm)
Temps: 75-80 air, 65-70 water
PPM: ~300 (~90ppm of cal/mag) using BluMoon nutes (local company)
Using 2ml/gal Hydroguard
Roots are crisp white, no smell. Leaves are a nice even green, no signs of nutrient imbalance.
I did have a slime issue with one of the plants a few weeks back but Heisenberg's tea cleared it up.
Just changed water on Saturday, ppm'd just above 300ppm and since then, PH has been dropping from 5.8 to 4.8 each day. PPM's have also dropped ~60-70ppm since feeding.

This is how I understood the PH/PPM relationship:
PH+/PPM- = normal, plant taking up nutes fine
PH-/PPM+ = Overfeeding, plant putting nutes back into water
PH-/PPM-... no idea.
So what would be causing my ph and PPM to drop? Like I said, plants look fine and are growing like crazy, just no idea what steps to take next aside from adjusting the PH everday.

Doesn't RO water use salt to filter the water? I don't know what your problem is because I've never seen this happen. However, 300 ppm seems pretty low to use as many people use 500 or more. Your success with any fert depends on the fert and plant strain and grow method. Does the fert you're using have pH buffers that might deplete? There might be something about your mix that is changing chemically and causing your water to become more acidic. If you want, it might be a good idea to try a different fert. I think supernatural has pH buffers in it. If you scroll down this, you'll see the hydro chart. http://www.supernaturalbrand.com/feeding-program/
I'm guessing that your ppm drops because of the fert uptake, but unsure of the pH. 80 degrees is kind of warm and this might have a role in what's happening. Wish I could help you more.

if your ppm drops it means your plants feeding ....... Top up with more

it could be ^^^ said about the mix of nutes, i don't know this for sure but iv heard some just don't like being mixed with and send the ph all over the place .

what are you useing for ph up/down buddy ?

edit: and what r u using as a ph meter ?

polishpollack said:

Doesn't RO water use salt to filter the water? I don't know what your problem is because I've never seen this happen. However, 300 ppm seems pretty low to use as many people use 500 or more. Your success with any fert depends on the fert and plant strain and grow method. Does the fert you're using have pH buffers that might deplete? There might be something about your mix that is changing chemically and causing your water to become more acidic. If you want, it might be a good idea to try a different fert. I think supernatural has pH buffers in it. If you scroll down this, you'll see the hydro chart. http://www.supernaturalbrand.com/feeding-program/ I'm guessing that your ppm drops because of the fert uptake, but unsure of the pH. 80 degrees is kind of warm and this might have a role in what's happening. Wish I could help you more.

Click to expand...

Thanks for the response! I don't think these nutes have any buffer built in, not like Advanced anyways. The hydro store near me makes/distributes them, and up until now they've been fine. Employee said they're comparable to GH and I figured I'd give them a shot to support a local biz.

I adjusted the PH this morning and so far has remained stable. I also bumped the PPM up to ~350 since I've read increases should be done within 100ppm at a time. As far as temp goes, my tent is in my garage so I'm doing my best to keep things cool without an AC unit. Typically stays around 77, peaks around 79-80 when it's the hottest. Water stays under 70 and I hit it with an ice bottle when needed. Buckets are all thermal wrapped though so it stays pretty chilled. Thanks for the link on that feed schedule too, I've seen a few similar to it but have mostly been trying to adjust based on the plants' feedback.

stinkyjoe said:

if your ppm drops it means your plants feeding ....... Top up with more

it could be ^^^ said about the mix of nutes, i don't know this for sure but iv heard some just don't like being mixed with and send the ph all over the place .

what are you useing for ph up/down buddy ?

edit: and what r u using as a ph meter ?

Click to expand...

I'll be watching to see how these nutes continue to behave going forward. Being that they're from a local company, there's next to nothing online about them. I'm using GH's PH up/down, and never mix the two in the same batch of water as I've heard that would produce salt buildup. Also using a BlueLab PH pen, freshly calibrated last week. I give it a solid couple mins to dial in when reading as it seems take that long to finally get a steady number. I'll keep y'all posted...