pH of nutes rises from perlite?

[DoctorWho]

I thought my plants were hungry so upped their nutes and noticed them starting to burn.  I checked the pH of the water in the trays and it had risen from around 5.8 to 6.5 - 7.0.  I'm using pH drops so I'm not 100% certain but those numbers would be really close.  Today I flushed the plants with a little bit of super low pH water to even out the high pH in the perlite and then gave them all a ton of water pH adjusted to around 5.7 and made sure that the run off measured exactly the same before putting them back in the tent and giving them all a feed.  I checked the water before giving it to them and it measured 0.6 EC and around 5.7 pH and after giving all the plants a feed I checked the run off in the trays which measured at 0.6EC and around 6.3 pH.  I'm going back down to the garden in an hour or so, dumping the trays and giving them all a reduced pH feed so when it climbs back up its in the right zone for good growth.  I'm just sore now so it needs to wait a bit.

 

Is it normal for perlite to do this? I thought it was inert which had me thinking it was my water but I tested it not even 5 minutes after it left the tap and maybe 3 minutes after going through the perlite so surely that wouldn't be enough time for chlorine or anything to evaporate.  I also doubt the plants are eating anything as the EC is exactly the same so does anyone have any idea whats going on?  I'm pretty sure watering at a lower pH will solve the problem but this is driving me bonkers

[Faith]

Hiya Doc I'm not sure but I have a theory?  I am having some slow weird stuff happening with a couple of seedlings I have going.  Not sure on the perlite but with my coco, and the o/n temps not being optimal, they aren't hungry like you said and then the buildup occurs, changing ph AND concentrating anything the perlite (in my case coco) has held on to...like the temperature slowing down the uptake kinda  I guess?  as mentioned I haven't used straight perlite as my medium so It's a stab, but how's the temps?

....if that makes any sense whatsoever doc

 

Peace. v

Edited August 19, 2013 by Vinno

[Bentato]

Perlite is not an inert medium (per say.. its depends what your definition of inert is), its actually on the alkaline side. Its really important to flush the hell out of it before you use it to get rid of the fine powder which will have a big effect on your PH. Even if you do flush your perlite before use then it will still have a upwards effect on your PH but not as bad as if you did not.

 

 Did you flush your perlite before using it ?

[DoctorWho]

Hiya Doc I'm not sure but I have a theory?  I am having some slow weird stuff happening with a couple of seedlings I have going.  Not sure on the perlite but with my coco, and the o/n temps not being optimal, they aren't hungry like you said and then the buildup occurs, changing ph AND concentrating anything the perlite (in my case coco) has held on to...like the temperature slowing down the uptake kinda  I guess?  as mentioned I haven't used straight perlite as my medium so It's a stab, but how's the temps?

....if that makes any sense whatsoever doc

 

Peace. v

I had the pH rise with the girls I had in coco but never had any issues with it because of the temperature.  As it got colder it just meant I had to water less often as the water took longer to evaporate.

 

Perlite is not an inert medium (per say.. its depends what your definition of inert is), its actually on the alkaline side. Its really important to flush the hell out of it before you use it to get rid of the fine powder which will have a big effect on your PH. Even if you do flush your perlite before use then it will still have a upwards effect on your PH but not as bad as if you did not.

 

 Did you flush your perlite before using it ?

Thanks spud, I'm think that explains everything   I flushed the crap out of the perlite from the get go.  To control the dust I sprayed water on the perlite as it fell into the pots and then I went to town hosing the crap out of the pots before giving them a final flush with pH adjusted water.  Even still though there has been perlite dust around which has gradually been decreasing with every watering but not going away entirely which would explain the massive instant swing in the pH.

 

In any case I watered at around 5.3 and it came out at around 5.7 earlier so the problem seems to be solved for now.  I'll just have to keep an eye on the pH in the future as the levels of dust could drop making me need to up the pH again but for now everything seems to be in order

[pegz]

What do you use to adjust your pH?

[DoctorWho]

phosphoric acid labeled as pH down from the hydro shop.

[The Stoned Jester]

if your a cheap-ass like me - Lemon juice works as well

[pegz]

Yeah, I thought he might be using vinegar or something.

[DoctorWho]

I think my problem was either not flushing enough before use or that more perlite dust is being made as time goes on.  Might even be a combination of both but I got it sorted out now by making the nutrient mix a bit too acidic so the perlite adjusts it back to the sweet spot for me