A Community and Forum For Aquaponic Gardeners

Growing Media

I was wondering if anyone had any idea if washed half inch broken sea shells would work for a growing media. The expense for non-limestone rock in south Florida is high and I don't know how adversely the limestone would affect pH.

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Permalink Reply by TCLynx on August 5, 2011 at 7:24am

Lime stone would cause you too high a pH to be happy about.

I don't really recommend the washed shells either unless you really love watercress. I went and used washed shells as about 40% of my media in my big system. pH generally stays at 7.6 or above if I add well water. This has made for very stable pH but it is problematic for the plants. At the higher pH I regularly need to use chelated iron to combat iron deficiency. Also, with the excess of calcium in the water because of the shells, my plants also have trouble getting as much potassium and I think they want since excess calcium can lock up potassium. Mind you, that system still works but not as well as it should. Watercress loves the alkali water though and during the cool part of winter grows rampant in my system.

Permalink Reply by TCLynx on August 5, 2011 at 7:25am

How much is the 1/2" brown river rock there as compared to the washed shells or the lava rock?

Permalink Reply by Bob Gee on August 5, 2011 at 7:43am

I am not sure. Getting ready to make a trip to the local stone distributor. The have peat rock which I didn't know if that would work either. The 3/4" eggrock is $120 per ton. The peat rock is $44 per ton. They have 3/8" granite, and 3/8" pearock but no 1/2" river rock.

TCLynx said:

How much is the 1/2" brown river rock there as compared to the washed shells or the lava rock?

Permalink Reply by TCLynx on August 5, 2011 at 8:03am

You might take some vinegar and a cup with you to run some tests with.

What is peat rock? hum precursor to coal, not sure about using that.

3/4" egg rock? I'm not sure what that is. Size would be right but $120 per ton sounds a bit steep.

3/8" seems a bit small but granite would probably be good for aquaponics.

3/8" pearock, uh pea gravel only describes shape but doesn't tell us what it is made of.

If you can find anything in the 1/2"-3/4" I recommend testing a hand full of it in a cup of vinegar (best if you can rinse it off first so that dust doesn't skew the test) and see if it fizzes big time. Limestone or calcium carbonate will fizz showing that it is dissolving in the acid and would have a buffering effect on your system and likely keep the pH too high.

Quartz type rock is generally good

granite or basalt may do

Also the light weight red lava rock, pumice or what the Australians call scoria is good though tough on the fingernails.

By the way, the washed shells are better than the limestone but I still don't recommend either.

Permalink Reply by Bob Gee on August 5, 2011 at 8:14am

Thanks for the insight. We are planning on taking some vinegar with us to determine what will work. Will let you know what happens after we get back.

TCLynx said:

You might take some vinegar and a cup with you to run some tests with.

What is peat rock? hum precursor to coal, not sure about using that.

3/4" egg rock? I'm not sure what that is. Size would be right but $120 per ton sounds a bit steep.

3/8" seems a bit small but granite would probably be good for aquaponics.

3/8" pearock, uh pea gravel only describes shape but doesn't tell us what it is made of.

If you can find anything in the 1/2"-3/4" I recommend testing a hand full of it in a cup of vinegar (best if you can rinse it off first so that dust doesn't skew the test) and see if it fizzes big time. Limestone or calcium carbonate will fizz showing that it is dissolving in the acid and would have a buffering effect on your system and likely keep the pH too high.

Quartz type rock is generally good

granite or basalt may do

Also the light weight red lava rock, pumice or what the Australians call scoria is good though tough on the fingernails.

By the way, the washed shells are better than the limestone but I still don't recommend either.

Permalink Reply by Bob Gee on August 5, 2011 at 10:38am

TCLynx...where do you get your gravel and how deep are you beds?

Permalink Reply by TCLynx on August 5, 2011 at 1:13pm

Keep in mind I'm in Central FL a bit North of Orlando.

There is a place in Sanford Florida called Pebble Junction which is a rock lovers paradise and I have gotten two dump truck loads (6 ton each) from there.

I have also picked up stone from a place near me in Mount Dora called Florida Natural Stone but that was more for convenience since they are only a couple miles away. I suspect that most of their stone supplies may actually come through pebble junction as well.

Most of my grow beds are 24 inches deep, I tend to use the 100 gallon rubbermaid stock tanks since they give me lots of filtration for the cost per gallon (the 12 inch deep 50 gallon stock tanks cost almost as much and then I would need to build a stand to put them on if I wanted them up at a comfortable working height.)