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Rising Ph - Aeroponics - Driving me Nuts!

C

cmpman1974

I've read some stuff on this, but am looking for opinions here. I recently tried building an aeroponics system. It is going OK, but I'm having major issues keeping Ph in the 5.5 - 6.0 range. My tap water is 7.5-7.8. PPM using a TDS meter is around 150 straight out of the tap.

I use Ph down powder. and get it to 5.7. I come back the next day...it's 7.5. Do the same thing...next day..up again to 7.0. Nothing stops it from rising. I pre-conditioned rockwool cubes and only a couple of spots are actually using rockwool. The other Root Riot cubes.

I adjusted Ph after putting in my nutrients. My PPM went up to 550 after adding nutes, which is where I wanted it. Now 5 days later, the PPM rose to 770. HOW?

This is a pain in the ass. lol.

Chris
 
I got it off Ebay and it says 'factory calibrated', but it's a cheap one so who knows? I'm using X Nutrients Grow and X Nutrients Micro.
 
ec swings are not uncommon. how large are these plants? do they drink lots?

as far as the PH goes, its concievable there is too much nitrate, even a little ammonium like 1:100 will keep the ph more stable.

however if your having these problems with unestablished new plants, there is probably something else going on.
 
If this is a new solution, chances are that it wasn't completely blended when you measured it the first time. I'll let mine run for an hour or so with the air and water pumps stirring everything up real good before I get a reading I can trust.

[background=rgb(255, 244, 228)]ec swings are not uncommon. how large are these plants? do they drink lots?[/background]
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In my exp, this is not the case. if the meter isn't broke, you should be able to get a reasonably close result day after day as long as the plants aren't drinking a good percentage of the water. Keep in mind that the plant uses the nutes and water so the readings shouldn't be the same, but after measuring for a few weeks, you should see a pattern.
 
Jeff H said:
If this is a new solution, chances are that it wasn't completely blended when you measured it the first time. I'll let mine run for an hour or so with the air and water pumps stirring everything up real good before I get a reading I can trust.



In my exp, this is not the case. if the meter isn't broke, you should be able to get a reasonably close result day after day as long as the plants aren't drinking a good percentage of the water. Keep in mind that the plant uses the nutes and water so the readings shouldn't be the same, but after measuring for a few weeks, you should see a pattern.
Click to expand...

especially with an ec that low i would not think it would be normal either. however with higher ex and large well established plants, i have not only seen the ec rise, but rise very very fast.
i had dwc toms my first time ever growing... they eventually drank like a gallon a day and would swing the ec very dramatically. you had to pretty much just add back tap or RO water because it was clear that they were consuming far more water than nutrients.
im not 100% why this is, but it definatly does happen.

on the other hand with my aero system, you would notice a very large drop in ec from the runoff water, when compared to the mist water.

my problem with the bad meter assumption is that they are so stupid simple to build, its hard to build a bad one. Ph meters are another issue entirely, but ec meters are very very simple devices and are not prone to wild fluctuation like that.

i am of corse assuming he is using a simple pen type... NOT the type with the two long metallic probes that you are supposed to put into the soil. those are IMO criminally bad, and are a joke.

he is also using citric acid which is a big problem, especially w/ respect to cost. citric acid is terrible for controlling PH in an alkalne solution because its entierly too weak.
its also an organic acid. from what i remember, the conjugate base of citric acid is vulnerable to all sorts of micro organisms, hence it is rapidly destroyed. some how the reaction is pushed back to the left, and further dissociation of the acid is suppressed via common ion effect. this is what i remember reading about. im not real sure about the specifics, as its been a long ass time since i read about it. citric acid is basically made in a bio reactor... while the specifics of said process is beyond me, its not hard to imagine why its not stable.

i would at least move to phosphoric acid, personally i use HCl from the pool store... costs me like 8 bucks a gallon, with a gallon lasting well over one year. keep in mind that i go through probably 1000-2000 gallons.
 
My plants are on their second set of leaves..babies. I don't think they are drinking much at all.

I have one of those cheap electronic plastic probe pH meters off Ebay for $12. I did calibrate it multiple times.

My TDS meter is this one:

http://www.ebay.com/itm/280349439863?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

My pH meter is this one:

http://www.ebay.com/itm/380521533210?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
 
the PH pen is a problem imo. are you calibrating it before use? neither of these things are temperature compensated from the looks of them, therefore you MUST calibrate them in the same temp as the solution you are trying to measure.

i have no experiance with that ph pen, but i would be very weary of its readings until you can get a feel for how it behaves with respect to its calibration. its possible its perfectly adequate. on the other hand its possible its not going to hold a calibration for any period of time.
have you calibrated it, then a few hours/days later checked it again to see how far it drifted?

for hydroponic applications, TBH i personally just go with good quality litmus paper. ive also used those drops made by GH, the drops seemed to be easier to read. ive found that fluctuation of PH from batch to batch dont matter much, as long as were around 5.5- 6.5 im good with it. im not saying the plants will not benefit from better monitored ph, im just saying its not worth my time to worry about such things. ive done it both ways, and have not noticed any adverse effects.

to allay any fears you have about your instruments, why dont you experiment on them.

get a bottle of water, drop like 10 grams of table salt into it. dissolve it completely.
take a reading with the ec pen.
put bottle in frige for 48 hours or w/e you want.
pull it out, let it reach the same temp as the first measurement, and note any deviation.
make sure no bubbles on the electrode surfaces, make sure you wash it off with some tap or RO before each measurement.

im recommending bottled water and not tap, due to possibly dissolved co2 in your tap water.


for the ph pen, just do like i said above, calibrate it, then check it against the calibration soltuion some time later. if its reasonably close, its probably in good shape. when the pen cant hold a calibration for any time its time to chuck it.
you really should calibrate it before each and every use. make sure its calibrated to the very same temp as the solution you are testing.

also try a stronger INorganic acid, phoshoric is about the safest acid i can think of. while it is still stupid expensive IMHO, one of those little bottles of GH ph down is like 9 bucks i think.
the phosphoric acid GH sells is diluted such that you can probably use it to clean/store your contact lenses ( kidding) ... its stupid dilute. ive tasted it several times, and its actually not hard to see why its used so often in food. its pretty pleasant tasting.
sharply sour without any adverse mouth feel like you get with other stronger acids.
 
I see queequeg says that you're using citric acid for pH down? I would grab some liquid GH pH down. It has buffers in it to help keep the pH stable. Sometimes the nutrient buffers alone just don't cut it.
 
I will write more in a bit. Thanks everyone for the advice. I truly appreciate it. In the meantime, here is the Ph down powder product I'm using:

http://www.htgsupply.com/Product-pH-DOWN-dry-by-General-Hydroponics---2.2lb.asp

Is this Citric Acid? Is it not a good product in your opinions? I seem to need to use 1/2 tsp or more to bring Ph in 3 gallons tap water from 7.8 to 6.0, but as I said, it creeps again. I';m going to check Ph levels a few different ways to be sure my probe isn't messing with me. lol.

Chris
 
That is the same stuff I use, but mine is a liquid. Based on how little you need to change the pH, I doubt it is citric acid, but instead, something much stronger.

Again, make sure the solution is thoroughly mixed before you check.

I have the same pH meter and it works well. I check it's accuracy often by comparing the results to the GH drops and they give the same results every time I have tried.
 
ph down products that are a dry powder like that are citric acid.
there is no other suitable dry chemical usefull for droping ph in hydroponics that i know of. silicates and many sulfates will alter ph, but not as drastically as a good strong acid, also they will obviously add sulfate and silicates which may or may not be wanted.

the dry stuff is citric acid, the liquid is phosphoric.
 
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