This is just a very quick video post to demonstrate how easy it is to see the difference between media that will keep your pH too high and media that will probably work for Aquaponics.
A glass or clear plastic container
Some Vinegar (white or distilled vinegar will be easiest to see through)
A hand full of your proposed gravel
It’s that simple. Ask questions before you pay hundreds of dollars to have a truck load of the stuff dumped in your yard and then spend countless hours washing it and putting it into your aquaponics system only to later find out your pH never comes down below 8!!!!!! YOU DON’T WANT LIMESTONE. Don’t assume pea gravel is fine because that is what so and so uses across the country. Pea gravel only describes the shape/size so one guy might get granite pea gravel where granite is plentiful but in much of the country the cheapest pea gravel is gonna be limestone and that won’t work well for aquaponics.
It is hard enough to deal with hard well water and aquaponics, don’t go putting a buffering media into your system since you can’t correct that with acid. Well I suppose if you put enough acid in eventually the limestone will all dissolve away but that won’t work for fish or plants and it’s far cheaper to test some gravel before you buy it and if it isn’t appropriate, DON’T BUY IT.