"Egg Rock", "Colorado River Rock", and "Marble Rock" useability

[Kerry McMahon]

I went to a local water garden place to get expanded shale, but due to the tiny size of it (the big pieces were about 1/4"), I couldn't use it.  The salesman assured me that their pea gravel was pH neutral (I asked him 3 or 4 times during the conversation).  So, he talked me into it, but we discovered that they were out of stock.  He said that it would be in the next day.  Now, a week later, after being told every single day that it was coming in tomorrow, it has finally arrived.  Not only is it not pH neutral, its in smaller chunks than the shale (it's basically rocky sand).  Grrr.

Frustrated, I went to Lowe's.  They don't carry expanded shale or clay, but did carry lava rock, which, of course, they are out of stock of and won't have any until next week.  Maybe.  Grrr.  They do have other landscaping rocks though.  They have bags of "Egg Rock", "Colorado River Rock", and "Marble Rock".  It's my understanding that marble is as bad as limestone for messing up your pH, but I don't know about the others. 

Do any of you know what "egg rock" or "Colorado river rock" is or if it's usable?  I know, I will probably just need to take a container of vinegar to Lowe's and test them, but wanted to see if you guys had any previous knowledge of these (in case they are pH neutral, but have other issues that vinegar won't tell me about, such as containing heavy metals or other unwanted minerals).

My only other options (that I am aware of) are driving 25 miles (one way) to an aquaponics store "in-town" or to order off of the internet.

[Alex Veidel]

River rock is a commonly used media, but I think it needs to be tested for limestone. Give it the ol' vinegar test.

[Kerry McMahon]

I gave up and drove in to town to Third Coast Horticulture and bought the expanded clay balls.  Only got one bag of it rinsed off pretty good before the rain came and I had to stop.  That stuff has a lot of dust on it.  I need to find a better way of cleaning it.

[Kerry McMahon]

"I have a bucket with some hole drilled in it like a plant pot that works good to rinse media"

That was the idea I had too.  I just haven't gotten a chance to start drilling it yet.  Glad to hear my idea will work though.  :)

[Gillian Burrus]

How many bags do you think you would need from Home depot though?  

[Gillian Burrus]

It is the top 1/3 of an IBC, I was guesstimating. If the IBC is 275 gal, and I am cutting the top off , then there is about 200gal left.  My grow bed it approx. 36x36x10  I have found a light weight media that passed the vinegar test, though I am worried that it is too small for a bell syphon.  I will post a picture of what i found. 

[Kerry McMahon]

I didn't even know that Home Depot had expanded clay balls (Lowes doesn't).

Gillian, since you know the dimensions, you can find the gallons pretty easily.  Its 7.4805 US gallons per cubic foot.  So, for you, 36in X 36in x 10in is roughly the same thing as 3ft x 3ft x 1ft, or 9 cubic feet.  9 cubic ft x 7.4805 = 67.3245 US gallons.  Just say 67 gallons (or even 65 gallons if you want a more even number).

If Randall's estimate of the bags of rocks being 0.4 cubic feet is correct, then you would need 4 bags (9 cubic feet of grow bed x 0.4 cubic feet per bad = 3.6 bags).

[Kerry McMahon]

Randall, the bucket with the holes worked great.  I have a bunch of cat litter containers in the garage, so I drilled holes in the bottom of one, then set up 5 more with water in them.  Put the media in the one with holes then sloshed it around in the first water bucket, moved to second and repeated, and so on.  By the time I got the last water bucket, the media was nice and clean.  The last 3 bags of the expanded clay went much faster than the first one did.

[Robert J]

Gillian,

If you're still looking for expanded shale contact [e-mail] his company sells it to most universities and he can tell you who might have it near you.  In my case I had to drive about 85 miles with my truck, but i filled the bed for $200.  Shale is lighter than most rock, has more surface area for bacteria--but will be hard on your fingernails.  I filled two IBC grow beds, a small tub, and half of the bottom third of two barrel grow beds (I had hydroton for the top third). And also a 24" X 15' X 6" bed.  And still have a pile in my driveway.