I have read that citric acid is pretty poor as a pH down, no buffering and the effects wear off after a couple of hours, spash out on some store pH down and see if it makes any difference.

sillyboy
Well something is definitely wrong. I did notice some foam floating in the nutrient solution, that makes me wonder what else is in it other than the nutrients. Also you mentioned that you were using tap water (I think), that may be a problem as well.

I would do a couple of separate tests, one Just plain water, and another with nutrients in it. And keep checking the ph in those, with and without adding the pH adjuster. Although I have read that citric acid also does not last as long (not saying 2 hours is long though), but it may not be as effective to what ever the problem is.

I'm not sure what that foam is, and that has me wondering if that is a sign of a problem. I would also clean and flush the system (just because), what can it cost? Then re-add nutrients. Take notes (at least mentally), and see if the problem continues. Is it possible some chemical got into the system (like from cleaning it).

Also I mean no disrespect, but I have no idea what meter you are using, and if it's calibrated correctly or not. So I would simply need to say you may want to make sure there is no problems there, simply to eliminate it as a problem. I use drops myself (no calibrating needed).

Lastly I would wonder what would happen if you don't bother to add any pH adjuster, would the pH skyrocket, or top off.

Hello sillyboy,

Your rockwool is acting like a basic buffer that keeps on increasing your pH. Rockwool has natural basic sites that increase the pH of your nutrient solution and for this reason a previous treatment with an acid solution (or a pH 4 buffer) is VITAL before using this media.

I can tell you with a 99.99% certainty that this problem is because of the buffering capacity of your rockwool that wants to set your pH at around 7.5-8 regardless of your nutrient solution makeup.

You should TREAT rockwool before using it, otherwise you will keep on experimenting this problem. However if you cannot treat it now just keep on adjusting the pH and eventually you will neutralize the buffering capacity of the rockwool (although it can take you 4-5 weeks of acid additions). Since the rockwool buffering capacity is not "fast responding" you will need to adjust pH, wait for an increase, adjust pH, wait for an increase, etc.

In the future, you SHOULD ALWAYS pretreat growing media that has a strong natural buffering capacity. I wrote an article in my blog about this if you are interested (shown on the link below).

I hope this helps :o)

Best Regards,

Daniel

Here is a link that might be useful: Why Wild pH Swings Happen

I had a similar "problem" and it turned out to be a faulty meter. My 7.5 pH was actually about 2.5.

Mike

Thanks so much everyone for replies! Really appreciate it.

This morning the pH reads about 8.1... which does seem to be where it "caps out".

I just went and flushed out my system. There is quite a bit of... "slime" covering everything. Like, if I ran my hand down the intake tube, I could scrape off a teaspoon of slime (I assume algae). The "foam" homehydro refers to I believe was pieces of the slime/algae floating around. That doesn't sound normal :)

I just re-measured my water. Depending on which cheap pH meter you want to believe, its between 7.4 and 7.8. Speaking of which... any house hold items with a rather "known" pH I can use to adjust my meter?

Your slime could be slime mold, ubiquitous in municipal water piping. Slime mold can be controlled by H2O2.

I have a Milwaukee meter. It mostly sits unused due to it being horribly unreliable. Cheap little drops work consistently and need no calibration. A little FYI: Some meters are affected by fluorescent lights. Don't know why, but if you put a Milwaukee meter like mine under a fluorescent light, the reading changes significantly. It happens consistently with T5s, CFLs, and my kitchen light, which I believe is in the T12 catagory. It changes as much as 3 full points.

That's interesting Joe, I had never herd of the meters being affected by fluorescent light before. If I ever get a pH meter I will keep that in mind and try to test it to see how it reacts to different light. As I mentioned I use the drops myself (general hydroponics pH testing kit). The directions say to fill the vial half way and add 3-5 drops. But I fill the vial to 1/3 of that (1/6, about 2,3 or 4 mm) and use one drop. It gives the same color results, just less liquid in the vial. That way it lasts longer. The test kit only runs about $8 and lasts me about 6 months or so. Also you can use the drops as a back up to see if your pH meter is at least close.

I don't use a lot of rockwool, mostly just for seedlings, then I place the starter cubes in grow rocks or coco chips. From the videos it looks like that's what you mostly have also. Although I guess that not flushing the rockwool with an acid first could be an issue, I have never done that, and have never had a pH problem when using it. But perhaps not all rockwool is created equal either.

I am still having alot of problems.

Anybody see anything interesting in this water quality report?

http://www.cityofseattle.net/UTIL/stellent/groups/public/@spu/@ssw/documents/webcontent/spu01_005903.pdf

Well, for whatever reason... the bottle of "pond" ph reducer (citric acid) was super terrible, and the ph down from GH worked just fine. So, um... nevermind :-P