Backyard Aquaponics
A place to discuss aquaponics

Yup, that's a buffer. Exactly how they work
However, there is less limestone there after it has finished buffering, and your pH would be 7.699999999 instead of 7.70
so less acid, more often, especially if applied directly to the offending media.
If applied directly there should be less of a swing, as the acid will work immediately, instead of diluting in the water and acting as it's filtered.
But as I said, I'm in uncharted territory here.

And one of the reasons why we've advocated NOT using limestone media in any form...

But, as you say... you're kind of stuck with it... and IMO... you'll never buffer beyond 7.5...

Until it's all used up... exactly as Kuda says.... that's the nature of a carbonate buffer source... such as limestone... dissolves in an acidic solution until the pH gets to a point where the buffering effect ceases... i.e the solution is no longer acidic enough to dissolve abd release any further buffering material.

I never expected scoria to have buffering clay in it though
+1 for washing gravel, you never know what was crushed with it.

Just wanted to post a quick follow-up on my previous post. This is an aquarium, not an aquaponics system, but it's interesting and potentially applicable. For some inexplicable reason, I had super high PH, around 8.2 (Cross-checked the Ph at a local aquarium store and the guy whistled). I wasn't too worried due to an absence of ammonia/nitrates. The fish seemed fine and plants too; the duckweed was growing before my eyes. Still, I wanted to bring down the PH--but not fast due to all the problems described in the link I posted earlier. I put in a section of dead limb from the yard. In 7 days, the Ph has dropped to 7.2.

what type of tree was the limb from?

I've heard of aquarium people using wood for such things, just need to make sure it doesn't contain anything particularly bad for your fish. Some wood can tend to turn the water dark though so it must be kept in mind before you use it on a display tank.

Some woods will leach tannins. You can boil wood to remove some of the tannins.
Other woods leach evil stuff. Leachate from pine and pretty much anything termites wont eat will most likely hurt your fish.

The tannins are probably a big part of what helps adjust the pH down but then you get to see dark water.

The resins in many conifers are not to the liking of many fish. Hardwood is usually preferred for aquarium and usually after long soaking then drying then soaking again.

By the way. I have been running an experiment in the Pee Ponic system for quite a while. It has one bed with river rock (quartz base pebbles that don't affect pH) another bed full of sea shells as the media which does keep the pH up at 7.6 and then I decided to test out wood chips as media in another bed to see if I could affect the pH of the system down any. So far, all I did was turn the water really dark brown. The pH has never gotten below 7.5.

I did run that with some fish in it for a while. I don't think the chips hurt the fish though there was some domestic violence between the tilapia in the barrel system and it seems the larger female killed the other two fish. I don't like barrels as fish tanks because it is so hard to see in them when outdoors under the sky. Anyway, the surviving female did fine in that system for quite some time till I decided to put her back in with the rest. So, at least blue tilapia don't seem to have a problem with my free wood chip pile which is probably mostly southern live oak chips with a smattering of other things.

The wood chips stay much wetter than the gravel or shells of course and there is more wicking action so the surface is usually moist as well. Some plants may like this, others will not. Wood chips might be good for beds that are in particularly hot situations but won't get watered as often. The wood chips will break down over time and need to be topped up or replaced.

Many people use cypress mulch for outdoor drip feed hydroponics but I would test it's safety with the fish variety in question before trusting it to an Aquaponics system.

I've thought about this before but kept forgetting to bring it up. Just how good of a buffering agent can sea shells really be? I can go dig up some sea shells in the heart of Texas that have been in the dirt for thousands of years at least (maybe a million or more). At one point in history, all of this area was under water probably. Now I ask again, if the sea shells in the dirt have not diluted and eroded in rain, floods, and other weather in at least 1,000 years, what makes you think they would erode and dissolve to affectively buffer the aquaponics systems within the next few months?

You might want to run some tests on those shells to see what pH they buffer to (some things buffer to 7.6 and other things buffer higher.) If the shells you find seems to buffer only to 7.6, then after a good rinsing (provided you are pretty sure that no nasty contaminants has been dumped over them) they could make a good addition to a system. If they buffer higher, like 8 or over, then be sure to place them in the system in a manner that you can easily remove them if necessary to adjust the amount of buffering you are getting (filling your grow beds with a media that buffers over 8 might make for much frustration.)

I have washed sea shells in my system and they for the most part seem to buffer to 7.6 but they are probably pretty fresh off the beaches and about all that has been done to them is washing.

People have noticed that shell grit might not be an immediate fix for a system that has a drastically low pH. You might need to use something a bit stronger to help get the pH back up over 7 and then use shell grit as the buffer to help keep it there.

I would think Cypres was a nono. 1) it's Cypress pine is it not? 2) Termites leave it alone.

There's a difference to laying covered in dirt, and being exposed to "dampness" of ocassional (basically neutral pH) rain events...

And being constantly exposed to acidic AP water...

Trust us.... as TCL says... use of shell grit has proven to be a good "slow release" long term buffer....

There has been much discussion about pH and buffering over several years... a search will bring up many dedicated threads and "hits"...

Including a full chemical explanation of how/why it works...

It's a long standing technique used in aquariums, not just AP.
When shells are in the dirt, they're protected by the dirt. If the dirt is acidic, then the shells, will corrode a bit, bringing the dirt immediately around them to a happy pH. only during a good soaking will this protective layer dissappear, and the process will happen again
The protective layer of neutralised dirt, is similar to the coating of aluminium oxide that protects aluminium from corroding. Scratch it, and it will corrode more until the protection is gone.

In AP however, if the water is acidic, the shells will try to neutralise it, being that the water neutralised is continuously mixed with the acidic water in the tank, the shells get no respite, and will corrode until the water is neutralised.

The buffering effect can be measured using a kH test kit. Otherwise referred to as Carbonate Hardness.

As rupe says, for more detailed explanations, do a search, there is heaps of info.

I've read thru this thread twice, and I guess I'm dense ..... I didn't see an answer that I could use, AFAIK, ...... My PH is high, 8.0-8.2 from the tap after setting for a few days ........ I'd like to bring it down to a good level for lettuce, cukes, squash, beans and tomatoes ....... I don't want to use a bunch of chemicals and acids that I know nothing about, and I want to be as organic as possible. I'm 110 miles 1 way from a large city, so I need something that I can use that can be bought at a grocery store or hardware store which is only 35 miles one way. Lemon Juice and vinegar didn't last but a few hours, so I don't want something temporary ...... I need something that I can add and it will work over time, like the oyster shell does for TCLynx ...... can I add whole or cut lemons, oranges, or some other type of citrus, or is there something else that will work. I don't understand all the opinions about buffering, etc., I guess I need to do some more research ........