Bad Batch of Plant !t Media (LECA)

[Vlad Jovanovic]

Ok, so after using about 70, 45 liter bags of LECA (Lightweight Expanded Clay Aggregate) made by a few different companies, I've finally ran into bad batch.

Since early spring of this year, we've used about 30 bags of Plant it! brand LECA with no issues. Until I noticed a dive-bombing pH problem in one of our little hydro systems which could not be explained. At least not by anything logical while running the system under normal circumstances.

The media was the first suspect. So, I took some media (new as well as out of that system) and placed it in a bucket of clean R/O water that had a pH of 7.3 and an initial EC reading of 166 micro Seimens.

Over the course of one week, the EC ended up at 1428 and the pH was at 3.5

Day 1 EC 166   pH 7.3 (Baseline)

Day 2 EC 550   pH 4.8

Day 3 EC 975    pH 4.1

Day 4 EC 1150   pH 3.9

Day 5 EC 1219   pH 3.8

Day 6 EC 1283   pH 3.7

Day 7 EC 1330   pH 3.6

Day 8 EC 1428   pH 3.5 It may be safe to presume that (likely) sulfur (or some kind of sulfurous compound) within the clay is the culprit.

Just figured I'd put this out there...Has anyone else had similar issues?

[Vlad Jovanovic]

The Hydrofarm rep's have thus far, been really cool, and honorable in dealing with the few small hiccups we've had with defective merchandise, or items damaged in transport. Much to their credit as a company, this time was no different. They have agreed to replace the entire two pallets of "funky" Plant It media. Kudos to them.

Irregardless of water chemistry issues (high pH, KH etc...) a good AP/soil-less culture media such as LECA should still be chemically inert, and pH inert. Throwing unknown variables at a problem (especially when known successful solutions already exist) in the hopes of solving said problem is a pretty poor strategy to employ. You might "luck out" here or there, but generally, from what I've seen, that kind of "solution" usually causes more, or bigger problems than the one it "solved".

Production environments are generally not ones in which you want to be "experimenting" (guessing). Since I'm not in a production environment, I was able to keep a few of these "bad batch" systems going using carbonates, bi-carbonates, and hydroxides to battle the sulfur induced plummeting pH and make some observations.

Firstly, a 1000 or so ppm of sulfur in solution and what that does or doesn't do to a plant is for most of us a big unknown. I am certain of that because even in the scientific community it is an unknown. Results from S excess in terms of plant physiology can vary widely (though they seem to be able to take quite a bit of it with little "obvious" deleterious effects. (This mostly according to leaf tissue analysis and observation)...so it will depend...

Secondly, and more importantly for folks who are just trying to grow stuff successfully (and not so much interested in scientific curiosity)...what I got to see over time (and a relatively short period at that) was a tremendous amount of  calcium precipitating not only in the rooting medium, but on the plant roots themselves. Large crystalline structures of SO4- and Ca2+ (or mostly Ca2+) began to form on the root structures of the plants (and in essence choke off absorption of other plant essential elements, and likely O2 as well). The accumulation of colloidal precipitates on the roots was impressive (I've never seen that happen to anywhere near that degree before this). And eventually things got really, really stinky (rotten egg/hydrogen sulfide smell) and after we couldn't take the smell anymore, we decided to dump the plants and sanitize the whole sha-bang.

Your results may vary, as I doubt that every "Bad Bag" is as bad in quite the same way (quantitatively...sulfur content may vary from bag to bag...batch to batch)...So everyone, please feel to try it at home if you are so inclined (and by home I mean Home, as investors tend to get "pissy" when engaging in unnecessary undertakings that end up costing them boatloads in cash, labor and lost production time)...

[Jeff S]

I've heard of a media test with vinegar and was wondering if you use white or dark vinegar and what reaction are you looking for?

[Vlad Jovanovic]

It doesn't matter, the color of the vinegar...you can use any type of acid (doesn't have to be vinegar, it's just that vinegar happens to be what most folks have on hand) to test your media for limestone (CaCo3). You're looking for Alka-Seltzer type fizziness...if it fizzes the media is no good. It's a basic acid/base reaction, where CO2 is released and fizzes from the limestone portion of the rock brought on by contact with an acid...

[Jeff S]

Thanks Vlad. I'm setting up a new GB and am going to use lava rock for a base media and top it with hydroton. I have year old GB that has always run around 7.2-7.5pH. I'm thinking about transferring some of the Growstone in that bed to see if it helps keep the pH up a little in the new bed. My smaller syastems have always had extremely low pH.