Explanation for rapid ph drop in DWC??? Can't find a solution!

[NaturesMed420]

Hey everybody! Lookin for a little advice...

I am in a circulating 24x5 gal bucket system with 50 gal control.
Problem starting in week 4 of flower through starting week 7 now.
I have been running DWC for some time and can never remember using so much ph upper as its requiring now. Heres a few specs:

Air temp: 67 - 75
Res temp: 65 - 72

Plenty of air through the stones, using 115L pump per 12 buckets

Using GH 3-part nutes at recommended 5-10-15
-Been trying 5 ml cal-mag or 1/4 tsp epsoms, or combination. Any suggestions?
-Using 2 - 4 ml Bloombastic
-For the first time: Adding small amounts of Canna Rhizotonic. Could this be the problem?

Ph: Stays right around 5.8 using auto-doser

PPM: Have tried from 500 - 1000 hoping to fix this problem. When I dropped the ppm, the Ph stabilized for a couple days and then resumed dropping. I highly doubt they want it higher than 1000.

I use a "Tall Boy" sediment and chlorine filter which brings the starting ppm of my water to 100-120 ppm.

I read some posts which suggested a very complete replacement of nutes washing off with fresh water to ensure getting rid of any problematic bacteria. This did not help.

The only other idea I have found searching posts for rapid ph drop is that I have root rot. They are large plants growing through a trellis system and it's very difficult to look at the roots. However I don't suspect root rot because of my industrial air pumps, plus I don't smell it like usual.

My only ideas are:

Somehow the Rhizotonic is causing the problem and should be stopped. (seems unlikely, but I don't really know)

or

I am thinking of dropping my res and doing a new batch, GH and Mag only with an application of H2o2 or bleach to try to kill anything that might be causing my issues.


Any thoughts, experiences or opinions are greatly appreciated! Has anybody else fixed plummeting ph? Especially in DWC?

Thanks for your time!

 

[Airnut]

Kelly resently had the same problem..

http://www.icmag.com/ic/showthread.php?t=173048&highlight=drop+flower
Might be O2 shortage in your water? Dispite 115 L per 12 buckets.?!?

Did you change the sort you grow?

 

[Hydro-Soil]

Yep.... 115 / 12 = only 9.5l per bucket.... minus additional losses through valves and connections.


If you're running 1 gallon buckets, it should be close to enough.

DO issues are most noticeable after/around week 4 and beyond...due to increased need for oxygen during bud formation.


You're right on the edge of having enough DO though.... or your plants would have died weeks ago.



Stay Safe!

 

[Airnut]

Yep.... 115 / 12 = only 9.5l per bucket.... minus additional losses through valves and connections.


If you're running 1 gallon buckets, it should be close to enough.

DO issues are most noticeable after/around week 4 and beyond...due to increased need for oxygen during bud formation.


You're right on the edge of having enough DO though.... or your plants would have died weeks ago.



Stay Safe!

WOW! This might solve the reason i made a profile here!!
Been looking but havent found one explained like this though - yet!

Increased needs while budformation?

Im gonna fire 2 more pumps up right this minute..

 

[sammyz2646]

PH goes up raise ppm's, ph goes down lower ppm's

 

[Scrogerman]

There's only 2 reasons why this could be happening in my book bro!
1- Your Nutes are too hot
&
2-you have A Bacterial issue.
forget your res/controller temps, its the temps in the buckets themselves you should be worring about, check those, & if they are ok your nutes are too strong. How often does your system circulate per hour, i think 8 full cycles per hour is a rough rule of thumb but the more the better imo to help with temps in your buckets! Run some OXY+ aka H2O2(17.5% solution)at 5mls per 10 litres every '24 hours-only' for a week, this will kill all the nastie pathogens in there & fix any potential rootrot problems, ive seen this time & time again & it always one of the above two reasons, so if you run the H2O2 you know then you have a clean res at the end of running it for a week. Run it for a further week to make sure, its worth doing & has a host of other benefits too, thicker stems, greener lusher growth due to increased nute uptake,not to mentiopn the added DO(Dissolved Oxygen) you will see a change on a daily basis using h2o2, believe me man!
Hope this helps! Good Luck............Scroger!
BTW.....-
When i run DWC i run a Kam-Air 40-litres per minute(at 2 meters) compressor air pump & 6 x airstones in a 70 litre RES (Rubbermaid for 2 plants)-no buckets, rageing rapids styley & they go nuts, explosive growth! its incredible man! I fix a dedicated clip on fan right over the commpressor Air-Pump to keep it cool, which in turn makes sure i am blowing constant COOL air into my res. Pumps get hot after a month or two, especially after the roots have enveloped the airstones causing back pressure, which in turn makes the AirPump 'HOT',because it is having to work that much harder, Blowing HOT air straight into ones RES, so if i put the fan in the correct position, i can virtually control the temp of the Res with this tecnique & its almost as good as having a chiller believe it or not people! Food for thought!! Hope that helps too!
Clip-On Fan = £9.95
Chiller = £££££££££££££ = Silly Money, although they are worth their weight in gold imho!

 

[delta9nxs]

just thought i would throw this in to mess up the rest of everybody's day as you think about continuously counteracting a temporary condition.

"Influence of carbon dioxide on alkalinity
Carbon dioxide can change the pH of water. This is how it works:

Carbon dioxide dissolves slightly in water to form a weak acid called carbonic acid, H2CO3, according to the following reaction:
CO2 + H2O --> H2CO3

After that, carbonic acid reacts slightly and reversibly in water to form a hydronium cation, H3O+, and the bicarbonate ion, HCO3-, according to the following reaction:
H2CO3 + H2O --> HCO3- + H3O+

This chemical behaviour explains why water, which normally has a neutral pH of 7 has an acidic pH of approximately 5.5 when it has been exposed to air.
C

http://www.lenntech.com/carbon-dioxide.htm


this is a duplicate of a post i made on my ppk thread. d9

 

[delta9nxs]

I should add that this reaction occurs in pure water as a result of contact with ambient air.

If your nute package tends to drive ph down you can get an even lower reading.

If you also have any root decay it can really plunge. I've seen the combination of these effects drive ph down into the 3.7-3.9 range in dwc, rdwc, and bio-buckets.

 

[Scrogerman]

just thought i would throw this in to mess up the rest of everybody's day as you think about continuously counteracting a temporary condition.

"Influence of carbon dioxide on alkalinity
Carbon dioxide can change the pH of water. This is how it works:

Carbon dioxide dissolves slightly in water to form a weak acid called carbonic acid, H2CO3, according to the following reaction:
CO2 + H2O --> H2CO3

After that, carbonic acid reacts slightly and reversibly in water to form a hydronium cation, H3O+, and the bicarbonate ion, HCO3-, according to the following reaction:
H2CO3 + H2O --> HCO3- + H3O+

This chemical behaviour explains why water, which normally has a neutral pH of 7 has an acidic pH of approximately 5.5 when it has been exposed to air.
C

http://www.lenntech.com/carbon-dioxide.htm


this is a duplicate of a post i made on my ppk thread. d9

Very deeply technical Delta,
Just one problem with your analysis man, he stated that his starting ppm tap is 100-120 & where does he mention anything about Co2 or using it in any way! He doesnt does he?,he would surely be having to run Co2 in his grow &or through his Res solution for it to affect his PH this way, would'nt he, but wouldnt that make the PH rise HHmmm? i see your point, but dont quite understand it, Your complicating a simple issue like ive said i have seen time and time again, but thanks very much for the chemistry lesson dude, lol, Very interesting but i very much doubt your analysis has anything whatsoever to do with the OP's original question as to why his PH is dropping this way, its highly unlikely what youve said dude. I Run DWC, have for years man & its always one of the 2 issues ive mentioned previously, either fix temps in buckets & run h2o2 and watch it fix the PH issue &or Decrease ppms, I personally doubt very much it has anything to do with Co2 & Pure water in this case, but thanks again for the technical chemistry lesson & i will keep in mind what you have said, you never know there may come a day when it is acctually a problem with Co2 and PURE water! you never know lol!
To help us understand your point man, can you highlight the passage/passages in the link you've posted please. I cant see anything in that lot that confirms your point! sorry im a bit thick mate lol

 

[Scrogerman]

I should add that this reaction occurs in pure water as a result of contact with ambient air.

If your nute package tends to drive ph down you can get an even lower reading.

If you also have any root decay it can really plunge. I've seen the combination of these effects drive ph down into the 3.7-3.9 range in dwc, rdwc, and bio-buckets.

Doesent this reaction refer to solutions in a sealed enviroment or as i took it, a vacume? This is definately a new one on me & im defo gonna research this one further for what its worth, but, id remind you his starting ppms are 100-120 and this indicates it is not Pure!! Further, if a nute package was to drive PH down, does this not possibly indicate that ppm's are too hot/strong & need to be weakened off a little? Good Luck!

Please let us know Naturesmed420 if the H2o2 fixes the issue man?, my money is on either of the 2 answers i gave!

 

[Layedback530]

interesting post

 

[Scrogerman]

Delta dude!
ive read over what you said again & no man, it doesnt make any sense sorry man, cant possibly be a reaction to Co2 in this case imo, can you please list the reasons why you think it is this Co2 reaction?
Many Thanks......Peace........Scroger! .

 

[Haps]

Weeks 4-7 are the heaviest feeding weeks of the crop cyle, and e&f buckets are a dynamic system supporting very fast growth, during this period. My PH has always tanked during this part of the cycle, simply because they are feeding so heavily. I chased it for a few cycles, then resolved it. I resolved it by not adjusting my nutes and addback, I leave them at 7-8ph where they come in at, when I add back this high value water/nutes, it bumps my reses back up where I want them and I add zero ph up to do the job.

This may not work for you, but it shows another side to the equation.
H

 

[Scrogerman]

I do exactly the same thing, or at least a similar thing. As res levels drop, ppms tank-up, -Ph will drift down(if its manual add back and i dont get to it quick enough), so my add backs take this in to account & ppms get weaker as the level drop speeds up. Its the way we ride it ! In other words plain water or Nute solution(un-PH'ed)add backs take you back to where you started & reduces the chance of phosphate build up etc!(no phosphoric for dropping ph back down, minimilising the chance build-up)

 

[NaturesMed420]

Thanks everybody for your replies!
Scrogerman especially, it sounds like you have this down. I just bought some 30% H2o2 to dilute down and begin applying. I am also borrowing a friends submersible UV water filter tomorrow to drive at the same purpose of eliminating harmful microorganisms.

I tested the temp in the buckets and they aren't getting above 75, I believe this is acceptable...
As far as your other suggestion of too high ppm, is it possible that 500ppm is still too high? Seems illogical to me and I don't think I can go much lower. Hopefully the H2o2 and filter do the trick.

Also, I thought that my air pumps, at 115 liters, would be sufficient for 40-50 gallons each.
Is the consensus that I need more?

Updates to come...

 

[NaturesMed420]

Success!

After applying the H2o2 my ph has leveled out beautifully! However this does coincide with ppm levels dropping below 450, originally around 520 while ph was dropping. So for the true test I will raise ppm back to at least 550 to make sure its the H2o2 making the difference, I suspect this is the case.

In either case though, my ph doser has caught a break and my mind is at ease!

Thanks Scrogerman! I appreciate your wisdom immensely!

Will update on definite causation

Still looking for opinions or guidelines on volume requirements for DWC air pumps... If my 115 liter pump is sufficient to oxygenate approximately 45 gallons of nutrient solution? 2.5L/gal
Scrogerman mentioned using a 40 liter pump in about 18 gallons, around 2.2L/gal. So I am on par with that...

 

[delta9nxs]

You are right scrogerman, I wasn't clear enough for you to understand,. My fault entirely.


Quote from me in post #8.

“I should add that this reaction occurs in pure water as a result of contact with ambient air.

If your nute package tends to drive ph down you can get an even lower reading.

If you also have any root decay it can really plunge. I've seen the combination of these effects drive ph down into the 3.7-3.9 range in dwc, rdwc, and bio-buckets.”


in the first sentence I was a little vague. I just meant to express here that it occurs also in pure water, not that the reaction does not occur in “un-pure water” or even water loaded with roots and nutrients. In the other two statements I endorsed the theories that high nutrients and root decay can also drive ph down. This is why you're suggestion to use h2o2 is valid. But ,if you have to use h2o2 continuously, there is something wrong with the way you are operating the system. Or maybe the design of the system.

These three things, separately or together, can drive down ph. Notice I didn't say that only these three things can do it.

Also I was not talking about anyone using co2 supplementation. The reaction describes co2 from ambient air.

Naturesmed420 was asking for reasons that this can occur. I offered reasons.

Btw way, I, like you, also have years of active hydro experience.

Have a nice day!

d9

 

[Zen Master]

dont forget to calibrate your PPM and pH instrument. They DO get out of whack once in a while and can lead you to dump a lot of stuff in a reservoir that doesn't actually need anything.

 

[foaf]

I don't what your problem is, but using flora nova, especially in bloom, I have to add ph up every day to keep my ph in line. It will go to 3.0 if I leave it alone, and thats even with a new reservoir change, 50 lpm air into one big bucket, recirculating dwc that turns over the full volume (18 gallons) every 20 minutes, and turns over the bucket volume every 7 minutes. and the plant is growing crazy well and healthy. scrogerman mentions having too high of a ppm, I do run mine high (1200ish), and I havent considered, neither do I understand how that could affect it, but it may be the case.
if you are doing everything else correctly and your plant is growing well, then you just chase it with ph up. I also dont think you need to get uptight about exact ph, but I do try to stay between 4.0 and 5.0. seems low doesn't it/

I have been running lower since I saw a graph that shows nutrient availability in DWC. The graph is much different than the traditional graph that we have all seen that is based on soil. If you believe this graph, source then in DWC we can run lower ph, and in fact, as you get near 6.0 things start to suck.

 

[Scrogerman]

Foaf, It sounds like textbook nute strength problems your having there man! if your PH drifts down like this, especially on a daily basis & is more than .5(down) ie-.6 & more, not only does the daily adjusting cause unnessesary stress to your plants(fact), its a pita, why push when the plants dont need pushing soo hard, apply the correct ppm's or more a optimal level of ppms your yields would surly increase also. If you lowered your ppms your Ph should/will stabilise after just 2-3 days after each res change-out. 4-5 is low - very low & surely causing you some issues. Im interested in what your upto now so i'll have to take a peep at your grows dude! if PH drives down this way, like myself & delta9 have already explained it can only be one of 2 or 3 but usually 2 reasons & they are Nutes too hot/strong or you have bacterial issues! its a textbook answer to a textbook problem! interesting stuff man! Good Luck!
Ive found the best ph in DWC is in veg = 5.3-5.6 & in Bloom 5.5-5.8!, its always worked the best for me & anything outside of this range & it just doesnt work as well & plant health & yields really suffer!
I beg to differ with that chart too, ph above 5.5 dont cut shit! above 6 in my ex it may do though, but that would depend on the composition of your nutes & what ph they have been designed to be used at ! so that chart is again another crude piece of missinformation imo!
Thats over 10 years of trial & error in DWC speaking! I was into NFT before that & Soil before that! Gone full circle & getting back into Soil & looking at Coco which is new ground for me but it always come back to Flavour & taste & for me the best tasting Buds ive ever tasted came from soil grown plants! but thats just me! Good Luck with your projects all!