Why does ph drop when rez gets low ??

Running a 5 gal dwc bucket, and it holds about 3.5 gallons. So today I woke up and ph was at 4.9 when 12 hours earlier it was 5.8... My rez has about 1.5 gallons left... So why does ph drop when rez is low ??

Meast,
Anybody's gess regaring your particular setup. So much depends on the nutrients and additives. The primary buffer system in hydro is the nitrate/nitrite ratio. Could be one is being used more (I'm a little rusty in all the chemistry).

I had a Waterfarm way back to try out hydro. Same thing happened to me.

But have a look at your additives. some of them really screw with ph and as your res gets low, things can become more concentrated and all sorts of interactions can occur.

What nutes are you using?
JD

General hydroponics

From GH website...

The pH in my system drops below 4 every few days after cleaning and refilling. How do I increase the pH and stabilize it?
Answer: The easiest way is to continue adding pH Up. This is generally fine because the additional elements that are added are potassium ions. Potassium is frequently the highest element in hydroponic nutrient solutions. Sometimes pH crashes because of the presence of a large amount of microbial activity in the nutrient solution. This is usually a result of poor maintenance of the system due to infrequent nutrient changes or other stresses. The best way to avoid this scenario is to keep a clean system with adequate nutrition.

Meast,
Also...top up your res more frequently. I don't know you and don't mean to insult you. But you know to always add nutes and allow to stabilize...and then correct ph.
JD

Yeah ph always seems to go to 5.3 when the rez gets low, I will top off more.

Meast,
Sorry I don't have anymore ideas. maybe someone else will.
Cheers,
JD

Seriously? Okay, let's analyze this for a moment. You now have less water(volume), then before. So with less water you now have a more concentrated nute level, hence a drop in your PH. Sounds like you don't have a buffered nute to begin with. Most nutes these days are buffered so they will hold your PH.

twistedwords said:

Seriously? Okay, let's analyze this for a moment. You now have less water(volume), then before. So with less water you now have a more concentrated nute level, hence a drop in your PH. Sounds like you don't have a buffered nute to begin with. Most nutes these days are buffered so they will hold your PH.

Click to expand...

What do you use as a buffered nute ??

twistedwords said:

Seriously? Okay, let's analyze this for a moment. You now have less water(volume), then before. So with less water you now have a more concentrated nute level, hence a drop in your PH. Sounds like you don't have a buffered nute to begin with. Most nutes these days are buffered so they will hold your PH.

Click to expand...

Can any expert's verify the quote above ??

twistedwords is right IMO, whats happening is that your plant is drinking the water. your getting a higher concertration of nutes in the rez. that is lowering your PH.
how big is your plant in said system? it may be too big for that rez, also you should mix your nutes in your water first, wait 30 mins then set your PH, wait 30 mins and check
again. hope this helps.

yes if you haven't got a root problem like root rot its to much nutes in your water so your plants are drinking more water than nutrients, when you have not enough nutrients in res the ph will rise

I employ a system that tops up the res automatically. The top up rez is at or around 7 ph with no added nutrients.

Twistedwords wrote: So with less water you now have a more concentrated nute leve

Click to expand...

The plant used both nutrients and water and if the PPMs are correct for the plant...it will use both equally.

If the plant were just using water and leaving nutes behind...then at the end, you would have a ppm of perhaps 20,000 which obviously doesn't happen.

But like machead posted, if your nute levels are off...one or the other may be used more.

JD

the water evaporates and the fertilizer does not . so it messes with the ph. make ... kind of like salt water . the s alt is left behind when you boil the water. this is my best guess. so just keep it topped off every 2 or 5 days.

Meast,
I overlooked the evaporation issue. With the Waterfarm I mentioned...there was a lot because of the bubble pump that sprayed the nutrients continuously on top of hydroton. A DWC though is mostly covered, correct? Might not be so much of an issue. But from the posts...sounds like more frequent fills and a lowering of PPMs might control your problem. Does your bucket have a sight/drain tube on the outside like a hydrofarm? If so, you could monitor your PPM to see if it raises or lowers on a daily basis. And use that as a guage to adjust nutes.
JD

You can add buffers to stabilize pH if necessary as well...but you shouldn't need them with regular top ups as mentioned.

JohnDee said:

The plant used both nutrients and water and if the PPMs are correct for the plant...it will use both equally.

If the plant were just using water and leaving nutes behind...then at the end, you would have a ppm of perhaps 20,000 which obviously doesn't happen.

But like machead posted, if your nute levels are off...one or the other may be used more.

JD

Click to expand...

not sure about this.. plants will drink just water and nutes when they want. if you watch your PPM's im sure there going up as the PH goes down. thats whats causing the drop in PH. i think we could use some more info, like how big is the plant? is it in flower or veg? if you have a large plant in 3 1/2 gallons it going to be sucking down water fast. if its vegging take clones to keep it going, kill it off and start a new mother from the clones. but i woulnt flower in that rez or your going to be fighting with it the whole time.use a bigger rez if your going to flower said plant. bigger res = stable PH.

Meangreens69,
Ya, I gotta admit, I'm a little rusty. Thanks for the polite correction of info. Been away from growing for 5 years. Environmental factors such as high heat, close lights and low relative humidity would certainly cause increased transpiration causing the plant to uptake water more then nutrients. It does get rather complicated and I apologize for my inaccurate or incomplete posts.
JD

no worrys JohnDee just trying to get this guys plant up and running.