Rapid pH Drop (5.9 to 5.5 in 4 days) a problem?

Discussion in 'Hydroponic Growing' started by farm Boy, Nov 30, 2011.

  1. Hey all,

    For details on my system on the grow so far, check my journal.

    The following is a brief rundown:

    Homemade Aeroponic system (recirculating)
    10 gal rez
    2 plants
    4 days into bloom
    RO water
    just switched nutrients from GH to X Nutrients (free samples at the local shop)
    Running 80% of the manufacturer-recommended nutrient dose (3 part, no supplements).
    920 ppm on day 1 of bloom
    990 ppm on day 4
    pH has dropped from 5.9 to 5.5 over this period.
    System used about 1.5 gals of water over the period

    While using the GH flora nuts, the pH would drift a little. But since switching to the X Nutrrients, pH seems to be in free fall.

    Plants healthy and show no signs of deficiencies

    So here are my questions:

    Should I be concerned that the pH dropped .4 in 4 days?

    Does this drop signal a possible problem in the system?

    Is this fall more likely the result of cheap nutrients that are not fully buffered?

    Thanks for the help,
  2. Hey Farm Boy,

    I'll start out by saying, I wouldn't personally switch nutes mid run. I'd especially not test out new nutes in a production run. And finally, on that note, I use GH FloraNova line, exclusively, because I feel they're the best for my plants, at a reasonable cost, and perhaps the most complete nutrient I'm aware of.

    That out of the way, this doesn't seem like an unreasonable drop over 4 days time, Especially switching into bloom.

    Are you 4 days into 12/12, or 4 days after plants showing sex? There's a difference!

    do you do a complete nute change at regular intervals?

    Always measure PH after you've topped off your rez with fresh water.

    PH dropping means a few things are happening. Any one of these will have an effect, it could be some, or all:

    1) Plants uptaking/transpiring more water, than they are using nutes, which will make your PPM go up. You need to top off with fresh water more often (daily, minimum), and can safely drop your PPM a bit, because your plants are getting plenty of nutrient already, you won't be depriving them of anything.

    2) Plants are using up dissolved oxygen in the water faster that your air pumps can put it in. To remedy this, add more oxygen by:

    A) increase the amount of air in your bucket. More pump, not just more airstones. You need at lease 1watt of air pump power per gallon. So 4-5watt pump PER 5 gallon bucket, or probably like 8watts total (2x4watt will do!) for your 10 gal rez. You may have omitted an air pump, due to your low pressure sprayers oxygenating the water. If this is the case, perhaps one 4-5 watt air pump will do the trick.

    B) Cool your reservoir nutrients, this will allow the water to hold more dissolved oxygen, which your roots need. These should stay between 65-70. I keep mine at 68, always.

    Note, check your roots, are there any signs of root rot? If so, see number 2, and do A and B, ASAP)

    Let me know if that helps at all.
  3. Hey OP,

    Helpful post. Thanks.

    Regarding switching nuts. I hear people say not to switch. But I've never heard why. What's you take?

    I switched 'cause I the Lucas formula wasn't providing all my girls needed and I had some free samples on the shelf. A pretty lousy reason, I know. But with the exception of the pH drops, it seems to be working well.

    I'm now five days into 12/12.

    The system was fully flushed at the switch.

    A 2-output (6 watt) ecoplus air pump pushes O2 to a 1-foot aquarium stone in the reservoir. The water never gets above 68F. And lately, it's staying in the low 60s. But from what you're saying, my air pump is a little weak.

    But the roots are in a rail above the reservoir. Man, I hope there's not a root rot problem.

    Now that the plants are groing into the scrog rack it will be hard to check the roots. But I'll give that a try.
  4. When you say the roots are in a rail, I'm not sure what you mean by that. You aren't going to let them dangle into the DWC? That would give them more room, I'd think.

    My opinion about changing nutes is that it may stress/shock the plant unnecessarily. Basically just causing you to use more time to get back on track.

    I've never heard of Lucas formula not providing just about everything your plants need. You mentioned that there were no deficiencies, but also that it wasn't providing all the the girls needed. What was missing?

    Just last week, I had to add a bit of Cal Mag to my Lucas formula, and it seemed to do the trick. This is the only thing I've ever had to add though.
  5. Hey OP,

    This is a full Aeroponic system, so the roots are never under water. They are sprayed for a minute then allowed to dry out for four minutes, before being sprayed again. All solution that doesn't stick to the roots, runs back into the reservoir. Check the second page of my grow journal for some detailed drawings of the upgraded Exo-Aero Grow system. It’s pretty cool.

    They (who ever that is) say that this system grows roots faster in aero systems than in DWC because more O2 is available.

    Although there is an argument about true (high pressure) vs. fake (low pressure, like mine) aeroponics that I don’t want to get into. You can delve into that fray in the aeroponics forum.

    Not sure why a slight change in nutrient brand and the resulting change in nutrient ratios would cause shock. I'd think it would do just the opposite. It seems like a slightly different mixture might allow the plant to grab something it was missing before. But that's just a feeling, not supported by fact or research.

    Unfortunately true research in the field of weed agriculture is almost unheard of.

    This is my first grow. So I'm not sure why I was getting some yellowing of leaf edges early on. I checked the deficiency websites and didn't find my exact problem. The pH was right (5.6-6.0) and the environment was within acceptable limits.

    So I decided to make a change. Like when a manager pulls the pitcher. I had to do something...

    But very shortly after changing brands, the plants got healthier. There were other things going on as well. So I cannot attribute the change entirely to the nutrients.

    I know a lot of people use Lucas and swear by it. So it must work. My main problem with it is that plants generally use different nutrients during flowering than vegetation, and Lucas does not account for that change. I've never seen that adequately explained.

    Speaking of CalMag. I just added some MagiCal as well. Unfortunately it has a couple of % of N. And I don't want it. How much N does the GH Cal Mag have?
  6. I see, regarding your aero system.. Does it have enough ventilation to allow the roots to dry between cycles? I was considering building a high pressure system, before I built mine.

    Yeah, your thoughts about changing nutes are valid. Keep in mind that the Lucas formula is designed as a system... Part of the reason for only using Bloom and Micro nutes is to prevent the plants from having too much N in the end. Your plants won't be as green as someone using a high nitrogen nutrient. This directly affects the end results of your useable product. The more green chlorophyll tastes like grass, and is a harsh smoke. So they won't be super luscious green on Lucas formula. But because of this, you don't have to change your reservoir regularly, and you don't have to flush your plants, because there isn't an abundance of unused nutrients left in your water.

    The best thing about Lucas formula is the fact that it provides everything your plants need, as far as the nutrients at the root zone, aside from oxygen and water... So if your PH is dialed, it allows you to get your environmental factors dialed in, or to experiment with.

    Personally, I use the grow nutes in the first part of veg, and then top off with the bloom nutes.

    I'll have to check, later, but I believe the cal mag I'm using has 0%, or maybe .5% N. unfortunately it has sugar and molasses in it though.. Which is great for soil, coco, or even Hempy Buckets, but not recirculating systems like mine, and yours. I only used a bit, and am keeping an eye on my res. hopefully won't have anything bad happen. I'll get back to you about the N%
  7. OP,

    Sounds like we're on the same page regarding nuts. Lucas is a good starting place, but needs to be addjusted so the plant gets more N in the begining.

    regarding aero, the roots don't really dry up, they just have time to absorb the nuts and O2.

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