Finding untreated lava rock can b tough.
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Untreated? What do they treat it with?
I like the idea of lava rock. It has a very rough surface and is porous, and lighter than regular rock, so it should work very well. I will check that out if I can buy a small quantity to test - unless they are treating it with spider venom or toxic sludge! 
Ive tested rocks from my yard - 1/2" to 3/4" or so regular aggregate used on driveways - and it is PH neutral after rinsing. Kind of heavy and not a lot of wicking though. Other than the weight, it would work great in the E/F tote.
I considered mixing in some perlite, but I think I will just sift through my bag for larger pieces. I made a sieve by drilling holes in the bottom of a plastic tub and that works ok for the amounts Im going to need.
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Here’s one thing i found
Hey all, just wanted to add something to this quote. Lava rock once it cools, as it ages turns from red to black. It can take hundreds of years to make this change. The darker lava rock is the better it is for inert applications. Very dark or black lava rock is non-toxic (and inert) it is normally more expensive then the red because it is normally below the red in the quarry and more difficult to collect. All aged lava rock is PH stable. Black lava rock is just as good as any other hydro media. Red lava rock is not. Red lava rock can still has trace sulfer compounds that when wetted can cause excess sulfer dioxide. Although sulfer is a trace nutrient in most nutes mixes - excess is toxic to plants.
Herbus
It was back in 2004 i did research on hydro media. Can’t remember what it’s treated with. Now that it’s commonly used in bbq i’d just go with those.
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Interesting! Thanks for the info!!
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Red lava rock, scoria, is not treated. It’s sold at Lowe’s for about $3 For 1/2 cubic foot. Scoria has been recommended and used in no-till gardening for years and is perfectly safe IME. The stuff that may be treated is the stuff for BBQs, its also much more expensive.
I won’t even go into the many uses a plant has for sulfur…
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I had a very bad experience with red lava rocks, i used them for my first grow with local soil, i made a bed on the bottom to assist with drainage and everything was ok, until the roots touched the lava rocks at the bottom, i know this now. Unless it has been treated and rinsed/buffered and all, do not use them straight out of the bag. I made that mistake too.
Check it out, it was @Herbie, @Uncle_Al and @ryasco who saved that harvest for me.
Go here ======> MadScentist’s first grow failure.
The whole point of growing on plastic is not having to deal with pH fluctuations, which are so kindly provided by mediums specially like lava rocks. Not going agains’t you @ReikoX, i just don’t wanna see anybody go thru what i did.
I do know that on a no-till enviroment the lava rocks are used and produce great results, but i don’t believe they would work like hydroton or perlite does… On their own. Like the MBBR would.
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Ok, Google Krusty Buckets sometime and tell me lava rock won’t work I hydro.
Here I’ll save you some trouble…
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Ok, no i see bro. The point of the thread was to awaken curiosity in the community to grow in plastic in order to mimic mother nature with synthetic media, and see if it works or not, and if it does how good or bad it would be.
I take it back, lava rocks work just fine. I would have to argue that your lava rocks may differ from mine, because of obvious geographical/geological reasons. I might take a handful of the lava rocks here and wash them to see where they stand in respect to pH and EC, would you do the same? It might be interesting!
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Sorry, I thought this was a different thread. I got off-topic. I have some fresh lava rock here. I can try a few tests and report back. In soil, the pH and EC don’t really mater, so I’ve never done that.
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And my point was that precisely. I want to encourage people to use synthetic media in order to save nature, ironic as it might sound. But like anything in life, irony defines us too. Like the snakes poison serum for bites, comes off the actual venum they extract from the very animal that uses it. Our cure might be under our nose. The power of one is to do something. Anything.
I am gonna get me some fresh lava rocks and follow up on it, thanks @ReikoX!
Check it out, recognition from my peers
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We got love for you Uncle. 
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What? Someone doesn’t???
Ninety Nine
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LOL. Im not sure ironic is strong enough word for what you are proposing as a reason to use synthetic or plastic media Please dont take this the wrong way, but I dont think you have thought this through all the way
Your idea does not quite fit the typical conservationist recommendation, which would be to use natural, renewable products - like soil - in order to NOT use synthetic ones. One of my daughters is about as green as you can get, and I bet she would give you a hard time about using synthetic, processed, or manufactured materials so you could avoid useing soil - especially plastics that are made from crude oil
Soil is a natural, 100% renewable resource. Plastic is as far from that as you can get. Digging up dirt to use in your garden, or better yet, composting, would be the natural, conservationist way to grow. Soil is renewable and has the least impact on the environment. At the other extreme is using plastics that start with oil wells, use huge amounts of energy to produce, never break down, and have lots of toxic byproducts.
Somewhere in the middle are things like hydroton, vermiculite, perlite, and ceramics, etc, that are all fired in ovens and or machined or processed in some way, as part of the mfg process. These are all materials that require a lot of energy to produce and have nasty by products that occur during manufacturing. Of course, plastics are the worst, but none of them are 100% safe, or natural, or renewable resources.
That said, please dont think Im trying to guilt trip you in any way. I am not even close to a hard core green crusader. I grudgingly recycle, and try to save energy where possible - mostly to save money, not the environment. I am very much against pollution in any form - but - I drive a gas powered car and truck and own an outboard boat and gas lawn mower
Bottom line - I think using any of these products is perfectly ok in our grows. Its impossible to grow indoors and avoid using manufactured and artificial products in one form or another, so if it will save time, money, or grow better weed, Im all for it 
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By no means whatsoever, no way i take it wrong, thanks for your time. I mean to say if we were to use all the plastic abandoned in the sea and beaches and rivers to use as a media to grow crops, not just weed, we would clean the enviroment for good. Not making new plastic but using whatever is out there, like old bottles, toy boxes and such.
God forbid i would have to face that, you can’t win… LOL
It’s about breaking schemes and rethinking the world, if we always go the way they tell us, we will never get anywhere. It’s recycling if you think about it, long and hard.
Thanks for your candour brother overgrower. Nice of you to take the time and answer.
HppHrvst
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Just for fun, I got a cup of RO water, pH 7.0, PPM 25. I put a handful of lava rock in there and swisher it around until the water was red and muddy. OH 7.0 PPM 37. I thoroughly rinsed them and have them soaking overnight.
That being said, there are many types of lava rock from pumice to obsidian. The specific rock I am using is scoria, red lava rock sold at home improvement stores for landscaping.
https://m.lowes.com/pd/Kolor-Scape-0-5-cu-ft-Lava-Rock/50040758
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I can get a handful of those tomorrow, and do the same, Sunday everything is closed down here, religiously.
Ah, I misunderstood. That is something my daughter would agree with I think
Interesting timing with you pointing that recycling aspect out just now! I was literally, in just the last few minutes, trying to think of cheaper ways to get some plastic bits that might work, and it occurred to me I have a bunch of PVC, CVPC, and PET plastic pipe scraps that could be cut up into even shorter pieces and used as grow media.
Im thinking of cutting it into 1/2" long sections and mixing it with the aggregate I have and using it in my ebb/flow tote. The plastic would save a bunch of weight, and create more open space between the rocks for better airflow. The plastic pieces wont have the surface area of some of the ones you were talking about, so they would not be as good that way, but these will be recycled. The rocks will hold and wick water much better than the plastic, so the two different things would work together, each providing a plus factor to the whole - I think.
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Im looking forward to the results you both get. Im liking the idea of lava rock instead of the aggregate I have in my yard. I think it will be lighter, and more porous, so should work even better. Plus its pretty cheap
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Ive been looking on-lne at Lowes and Home Depot at lava rock. I wonder if the red landscape lava rock is died to make it more red?
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