Runoff pH 7+

[Grower2020]

Anyone have any problems with coco coir and runoff being out of range? All the scientists of coco who I have seen speak on run off suggest that the ru off should be within .5ph of what u put in . And if it's more than 6.5ph expect some iron lockout which is what I have seen recently . People saybp disregard ru off ph but now I'm seeing why it shouldn't be ignored. I did a slurry test on the coco also at the roootzone and it was 7+ exactly same reading as the ru off ph . Could it be a bad batch of coco that has aged too much and hav3 too much decaying coco in it causing a higher ph buffer to occur ? I tested a sample of some oth3r coco hygen coco coir lite and put some nutrients through it and check3d runofff and it came out only. 1 high3r than inflow ph . So I'm guessing there is some kind of problem with the coco itself causing an abnormally high ph buff3r basically neutral.
Anyone else experience this problem?

 

[Peat Phreak]

Yes. The problem is not specific to coco. It can happen with any media. When the plant uptakes nitrate, the roots will exude a base that causes the pH to rise. The pH will rise every time you feed. Even if you pH your feed to 5.8. Unless whatever microbes you happen to have in the media are acid producers or your nutes are heavy in ammonium.

I sterilize my media (peat) so there is no acid producing bacteria. I use minimal ammonium. The pH will rise the entire grow unless I use more acid and a lower pH than anything commonly prescribed for growing weed.

For example, I didn't pH my current grow to see what would happen. The runoff was 7.8 after 4 weeks of veg and a Manganese deficiency occurred. I was able to correct this high media pH by doing some heavy duty acid flushing.

I used citric acid and tap water pH'ed to 3 and flushed 10 gallons thru 5 gallon pots. The media pH reduced to the mid 6 range. Acid flushing is something that needs to be repeated once or twice a week for effectiveness. The repeats don't need 10 gallons. I give the repeat flushes enough citric 3.0 pH to get runoff. Then feed with a bicarbonate neutral nutrient solution. This can be with RO water or tap water with enough acid to neutralize the bicarbonate. In my case, that happens around 4.2 pH.

It took about a month to get the media pH under control. Less potent acid solutions were gradually introduced and less acid flushing was needed because the acid was starting to win the battle too well. The media got as low as 5.1 pH. Now I am back to normal feeding without acid pre-flushing.

The low pH inputs did not harm the plants at all. This is because the pH of the acid water instantly rises when it mixes with the alkaline media.

 

[Grower2020]

Yes. The problem is not specific to coco. It can happen with any media. When the plant uptakes nitrate, the roots will exude a base that causes the pH to rise. The pH will rise every time you feed. Even if you pH your feed to 5.8. Unless whatever microbes you happen to have in the media are acid producers or your nutes are heavy in ammonium.

I sterilize my media (peat) so there is no acid producing bacteria. I use minimal ammonium. The pH will rise the entire grow unless I use more acid and a lower pH than anything commonly prescribed for growing weed.

For example, I didn't pH my current grow to see what would happen. The runoff was 7.8 after 4 weeks of veg and a Manganese deficiency occurred. I was able to correct this high media pH by doing some heavy duty acid flushing.

I used citric acid and tap water pH'ed to 3 and flushed 10 gallons thru 5 gallon pots. The media pH reduced to the mid 6 range. Acid flushing is something that needs to be repeated once or twice a week for effectiveness. The repeats don't need 10 gallons. I give the repeat flushes enough citric 3.0 pH to get runoff. Then feed with a bicarbonate neutral nutrient solution. This can be with RO water or tap water with enough acid to neutralize the bicarbonate. In my case, that happens around 4.2 pH.

It took about a month to get the media pH under control. Less potent acid solutions were gradually introduced and less acid flushing was needed because the acid was starting to win the battle too well. The media got as low as 5.1 pH. Now I am back to normal feeding without acid pre-flushing.

The low pH inputs did not harm the plants at all. This is because the pH of the acid water instantly rises when it mixes with the alkaline media.

I also did the same thing and flushed the crap out of the media with 4.0 ph feed. I didn't go any lower because apparently the nutrients become damaged at a lower ph than 3.7 ph

 

[Grower2020]

I also didn't notice any bad symptoms when feeding this pH for a week straight .

 

[Peat Phreak]

I also did the same thing and flushed the crap out of the media with 4.0 ph feed. I didn't go any lower because apparently the nutrients become damaged at a lower ph than 3.7 ph

4.0 isn't low enough to make big moves. If you are using tap water, a pH of 4 is approximately where just enough acid has been added to neutralize the bicarbonate in the water. So the solution has almost no 'acid power' left over to reduce the bicarbonate in the media.

3.0 pH is where you have neutralized all the bicarbonate in the tap water AND you have extra acid in the water to reduce the media pH.

I'm not aware of damage to nutrients at a pH lower than 3.7. Where are you getting that from? I'll do some research. If it's a real thing, then acid flushing first followed by a normal feeding would be fine. That is what I do most of the time anyway. Especially in the beginning of the pH battle.

But I have been skipping the acid flush and have been doing an acid feed of 3.5 pH for the past three feedings. Media and runoff pH are in the good zone and nothing bad is happening.

 

[Grower2020]

4.0 isn't low enough to make big moves. If you are using tap water, a pH of 4 is approximately where just enough acid has been added to neutralize the bicarbonate in the water. So the solution has almost no 'acid power' left over to reduce the bicarbonate in the media.

3.0 pH is where you have neutralized all the bicarbonate in the tap water AND you have extra acid in the water to reduce the media pH.

I'm not aware of damage to nutrients at a pH lower than 3.7. Where are you getting that from? I'll do some research. If it's a real thing, then acid flushing first followed by a normal feeding would be fine. That is what I do most of the time anyway. Especially in the beginning of the pH battle.

But I have been skipping the acid flush and have been doing an acid feed of 3.5 pH for the past three feedings. Media and runoff pH are in the good zone and nothing bad is happening.

I wonder if all that phosphorus will be damaging in the long run though? To get the ph inflow down to 3?

 

[Peat Phreak]

I wonder if all that phosphorus will be damaging in the long run though? To get the ph inflow down to 3?

It might be a problem. Too much P can wreck the grow in a hurry. That is why I use citric acid for this. It does not have NPK.

 

[Peat Phreak]

I use 15g of citric acid per gallon to get down to 3.0 pH. That's a lot. How much other people would need to use depends on how much bicarbonate is in their tap water. My bicarbonate is approximately 75 ppm. The total ppm of my tap water is about 150 ppm.

Since citric acid is a so called weak acid, the ions do not completely disassociate. The leftover ions that are not useful for acidification are completely utilized as food by microbes. This makes citric acid a bio-stimulant.

 

[Peat Phreak]

I skipped the heavy acid treatment for this feeding to check the current status. They were fed at 5.8pH which contains some bicarbonate and will raise the pH a little. There are four different plants in two different stages.

Plants 1 and 2 started at 7.8 pH a month ago. Six weeks from seed.
Currently - Plant 1 is at 6.4 pH. Plant 2 is at 5.9 pH.

Plants 3 and 4 started in the low 7s a month ago. Four weeks from seed.
Currently - Plant 3 is at 5.7pH. Plant 4 is at 5.4 pH.

I will discontinue the acid treatment for a week and restart if needed. As far as I can tell, this heavy duty citric acid treatment works well to correct high media pH. You just have to use a lot of acid and spend more time on watering day for as long as it takes to get the pH down.

And it might not be possible to reduce it as much as I did if you are starting later in the grow cycle because there will be a lot more bicarbonate to neutralize even if the pH is at the same starting point as my example.

 

[Grower2020]

I skipped the heavy acid treatment for this feeding to check the current status. They were fed at 5.8pH which contains some bicarbonate and will raise the pH a little. There are four different plants in two different stages.

Plants 1 and 2 started at 7.8 pH a month ago. Six weeks from seed.
Currently - Plant 1 is at 6.4 pH. Plant 2 is at 5.9 pH.

Plants 3 and 4 started in the low 7s a month ago. Four weeks from seed.
Currently - Plant 3 is at 5.7pH. Plant 4 is at 5.4 pH.

I will discontinue the acid treatment for a week and restart if needed. As far as I can tell, this heavy duty citric acid treatment works well to correct high media pH. You just have to use a lot of acid and spend more time on watering day for as long as it takes to get the pH down.

And it might not be possible to reduce it as much as I did if you are starting later in the grow cycle because there will be a lot more bicarbonate to neutralize even if the pH is at the same starting point as my example.

I think I'm going to quit growing in coco . It can be a great medium but it can also be the biggest pain in the arse if something is not quite on point

 

[Peat Phreak]

I think I'm going to quit growing in coco . It can be a great medium but it can also be the biggest pain in the arse if something is not quite on point

Peat is easier to use than coco and cheaper to buy. Feed 15x a month. The safe pH range is 5.0-7.5. It starts at 6.0. Some people don't pH at all with peat. That doesn't work reliably for me. But it can work fine in some situations.

 

[Grower2020]

The thing I worry about with peat is overwatering and I'm a terribly guilty of it

 

[Peat Phreak]

You only have to water it once every other day. One big watering with 25% runoff and 1500ppm. I'm too lazy to water daily. It retains water better than coco.

 

[Grower2020]

You only have to water it once every other day. One big watering with 25% runoff and 1500ppm. I'm too lazy to water daily. It retains water better than coco.

Man I'm having hardcore trouble with my runoff still. I've got a flower tent that is going fine with runoff ph at 6.8-7.1 . It'd been that way for ages and no problems at all . Few burned tips etc from high flowering ec but no deficiencies at all and healthy fat buds . Then my other tent .... Iron or mag def I can't tell it could be both but I think it's iron from the high ph ru off. It's not higher than my flower tent ph wise but yellow between veins and seems to be worse at top of plant. Man I wish I knew exactly how to treat this

 

[Phytoplankton]

Pics might help. but a question, was the coco buffered by the manufacturer? If so it's normal that the runofff would be higher in PH than the input. If the plants aren't suffering then continue on. Now the plants with the upper leaves yellowing could be light bleaching, Iron, Sulphur, or Magnesium deficiency. Doubtful that it is iron, cannabis needs very little iron. In an iron defiiency the new leaves would start out yellow then slowly get a little greener from the edges in. My best guess would be a magnesium deficiency, a foliar spray of epsom salts would be my starting point

 

[Grower2020]

Pics might help. but a question, was the coco buffered by the manufacturer? If so it's normal that the runofff would be higher in PH than the input. If the plants aren't suffering then continue on. Now the plants with the upper leaves yellowing could be light bleaching, Iron, Sulphur, or Magnesium deficiency. Doubtful that it is iron, cannabis needs very little iron. In an iron defiiency the new leaves would start out yellow then slowly get a little greener from the edges in. My best guess would be a magnesium deficiency, a foliar spray of epsom salts would be my starting point

Magnesium is a mobile nutrient so it's not magnesium. It's definitely iron . And my friends grow in coco and their runoff ph isn't at 7 like mine is . Their ru off ph is within .1 of what they put in .

 

[Phytoplankton]

You're right on the mag, but the plants should grab the nutes they need in the PHed water you feed in, before the PH increases. Try iron and/or Sulphur and see what happens. Also, have you done any flushes? The other thing you also mentioned is it could be bad batch of coco that wasn't washed long enough and it could have too much sodium in it, but if the other plants are doing OK on the same coco that's probably not it.