Pea Gravel Media Problems

[William Sherman]

I was setting up a new system and went to a local nursery and purchased a trailer load of pea gravel.  The gravel really looked good, a mix ranging from 1/4" down to almost sand sized.  My wife and I washed the gravel until the water turned clear and proceeded to put it in our grow beds (GB).  We have a 250 gal food grade liquid shipping contain which I sunk into the ground, as a Fish Tank (FT).

We filled the tank with well water (ph 6.8) and added  aeration and fish.  We saw algae growing and felt we were home free.  We started circulating through our GB and suddenly we had the "red river" in our FT.  We couldn't see anything in the tank, so we drained it and got the fish out into clean water.  I got in and power washed the FT and started with new water.  My wife and I once again washed our gravel, 1 cup at a time and we started out again with clean GBs.  We also purchased a 5-way tester and began daily ph testing.  Mind you, we started with well water with a ph of 6.8.  Upon starting to circulate through the GB, we saw our ph start climbing.  We tried adding vinegar and ph-down, but nothing would get it back in range.  Shortly thereafter our fish started dying off and we finally lost them all.  Our FT remained pretty clear (a little cloudy, but could still see the bottom).  We are currently in a holding pattern, no fish and no plants in the GB.

We are pondering our next step.  We are considering doing another wash of the pea gravel to include a soak in pool acid before the final rinse to hopefully neutralize what ever is leaching out of the pebbles.  Has anyone out there encountered a problem like this and do you have any recommendations?

Frustrated in East Texas

[Richard Wyman]

How high did the PH get? Did you try to adjust too fast? Trying to change it when the gravel is buffering it can cause PH swings that could have stressed your fish. A high PH will probably affect plants more than fish in most cases.

[William Sherman]

The ph hit at least 8.4 (that was as high as our tests went) and no, I even used a little less of the ph-down than recommend at a time and waited 24-hours between dosing.

Richard Wyman said:

How high did the PH get? Did you try to adjust too fast? Trying to change it when the gravel is buffering it can cause PH swings that could have stressed your fish. A high PH will probably affect plants more than fish in most cases.

[Richard Wyman]

I have read that PH adjustments should not be more than .1 per day. One full point is 100 times less or more acidic/alkaline. If your gravel is buffering that strongly then putting in the PH down probably just bounced PH down, then it shot back to where it was.

Are you gonna change out your gravel and try again? So sorry to hear about your fish.

[TCLynx]

It might be time for some other tests/experiments before you go to the trouble of washing the gravel again.

First, you say the well water has a pH of 6.8, however, if you test the pH of tap water (well water or city water) immediately upon drawing it from the pipes, you are likely getting a false low reading. See carbon dioxide gets trapped and dissolved in water that is in pipes and holding tanks or even water from the aquifer. This carbon dioxide dissolved in water acts as a weak acid. As soon as the water gets to air out for a while, the pH will climb to it's real level as the carbon dioxide outgasses from the water.

My well water if I test it immediately out of the pipe or hose, will show a pH of 7. But if I bubble it for a while, the pH gets up to at least 8. So, just to help up sort out what the real problem is, first do a test of your tap water again. Draw some and bubble it for 24 hours and then test the pH again.

However, what worries me more is that your pea gravel might be limestone. If your gravel is limestone, acid is not going to help until you have dissolved all the calcium carbonate (that is what limestone is.) So dissolving all your media by soaking in in acid probably isn't a cost effective way to handle things. You might try pouring a cup of vinegar over a cup of your pea gravel and see what reaction takes place. If it bubbles and foams over (like a kid's volcano with baking soda and vinegar) then you might just want to replace your gravel. This time make sure you get something that is pH inert. Quartz and granite types of rock as well as river pebble of the right size are more likely to work for you. Lava rock also works for some people but I've never seen small size lava rock around here so I only use it in the bottom or around the drains of my grow beds.

You can't effectively use acid to bring down the pH of a system with strongly buffering media. I have washed shells in my systems and they buffer to a pH of 7.6 I have tried to bring the pH down with acid and about all I can do is keep my well water from bring the pH above 7.6. If I try to bring it lower with acid, it only works for part of a day before the pH bounces back up to 7.6.

So, if the problem is your well water actually having a higher pH than you think, then the acid added to your top up water and allowed to stabilize before adding to the fish tank can work. But if your media is limestone or marble or shells, you will not be able to bring down the pH with acid. The only choices are use plants and fish that like the really high pH or more likely, get different gravel.

[William Sherman]

Currently running some tests in mason jars. Started with well water at 6.8 or possibly lower, tester only goes from 6.8 to 8.4. Then added about 2 cups of triple washed pea gravel, stirred vigorously, let sit about 5-min and got a reading of 7.2 Now I'm just waiting and stirring occasionally. Will test again at 1, 2, and 3 hrs.

Then plan to put 2 cups of pea gravel in a pretty strong acid bath for about an hour, then rinse thoroughly, add fresh water and essentially repeat the above test. My hope is the acid bath will neutralize what ever is leaching out of the gravel and make it neutral. Only time will tell.

Richard Wyman said:

I have read that PH adjustments should not be more than .1 per day. One full point is 100 times less or more acidic/alkaline. If your gravel is buffering that strongly then putting in the PH down probably just bounced PH down, then it shot back to where it was.

Are you gonna change out your gravel and try again? So sorry to hear about your fish.

[TCLynx]

Hard to say if all of that is going to be the gravel or the water outgassing changing your pH.
If the gravel is limestone, soaking it in acid won't leave you much.

[William Sherman]

TC,

It seems as though I have both problems. My well water seems to jump around, when I first tested, it was a nice Ph of 6.8, but when I drew it again for this test, it was a Ph of 7.0. After aerating for about 12 hrs. shot up all the way to 8.2. Plus as you said, my gravel creates a mini volcano when exposed to a strong acid. However I did soak a batch of gravel in an acid solution, then washed it thoroughly and now it seems to hold at a Ph of about 7.0.

Upon close inspection of the pea gravel. it certainly does not appear to be limestone and the shell content appears to be no more than 1piece in 75 pieces. The gravel was heavily coated with a "red" settlement of some type, some of which washes off with repeated rinsing; but a whole lot more releases during the acid bath. The volume of gravel did not seem to diminish after the acid bath. Is it possible that red stuff is the culprit? Around here, even the bags of pea gravel being sold at Lowe's, have the red stuff dribbling out of the sacks.
Any other suggestions would be greatly appreciated.

TCLynx said:

Hard to say if all of that is going to be the gravel or the water outgassing changing your pH.
If the gravel is limestone, soaking it in acid won't leave you much.

[TCLynx]

Well, it is possible that your problem in the gravel could be some alkali clay sediment stuck to it. I think I've heard of people getting lava rock that had clay stuck to it that affected pH for a while.

Over time eventually, pH in an AP system does tend to drop. If you can get your well water adjusted down a bit and acid soak your gravel, perhaps you can get started with a pH somewhere between 7 and 8. Then over time your top up water might help to keep your pH from crashing down too low.

Good Luck with it and let us know your results after a bit of time. (Like you might take some of the gravel that you have acid soaked and rinse it then let it soak in some distilled water to see what the pH does over say a week.)

I remember back when I was first learning about Hydroponics and I didn't understand about the false pH readings from tap water directly out of the faucet. I couldn't figure out how the heck my pH kept rising when I was adding nutrient solution (which brings pH down) to water with a pH of 7 and then the next day it would be up around 8?????? Later I learned about the carbon dioxide in the tap water and how outgassing would show a true reading of the tap water pH and my water really had a pH of 8 most of the time. Well water pH will vary some depending on season and the amount of rain getting down to the aquifer the well water comes from. My well water comes from a limestone aquifer and the pH is usually around 8 or a touch above.

Even with my high pH tap water, once I managed to get cycled (original barrel system had river rock and no extra buffering) the pH did drop below 7 and kept dropping till I added a buffer.

I do kinda recommend doing your initial cycling "fishlessly" since you are having a bit of a high pH issue. High pH and ammonia are a deadly combination for fish. You can use an alternative ammonia source to cycle up and hopefully find the pH balance and once things are nice and stable, you can add fish and hopefully avoid the stress of cycling up with fish. You have already experienced the stress of fish dieing, so I don't think you need to repeat that right now. Time for some positive.

Good Luck with it.

[Frank Gapinski]

Hi William,
I hate to be a bearer of bad news but choosing gravel that is a quarter of an inch in size and smaller - all the way to fine sand grains is just asking for trouble. It looks nice at first. You think it should be ideal for Aquaponics but wait 6 to 12 months and you will have problems with your system.

The size of your gravel is just too small. You will slowly create anaerobic black zones where fresh oxygen will not be able to penetrate to oxygenate plant roots or microscopic bacteria. In fact anaerobic bacteria will colonize your system and other negative issues will arise.

Your dilemma reminds me of Murray Hallam's Aquaponics Secrets DVD trailer where Murray succinctly explains the very problem that you have shared with us all and how many people see his system and then reject his advice and do exactly what you have done. Choose gravel that they think plants will like....

See this link for a hint and an explanation of your problem:

http://www.youtube.com/watch?v=btUZBk8G1xk

You really need to get rid of your pea gravel.
Toss it out completely and get 20mm gravel or small pebbles about an inch in diameter.

I know this sound extraordinary but you need to create air pockets in your gravel grow bed system for oxygen to penetrate.
For worms to wriggle through...
For plant roots to penetrate and thrive...
Spaces for air pockets is crucial.
Hard to believe but this system that Murray has created will enable you to grow plants for over 4 years without cleaning the grow bed system and to it enable you to enjoy your Aquaponics journey with a trouble free system.

Cheers
Frank

[TCLynx]

I guess I hadn't paid very close attention to size on the gravel. My gravel is 1/2" brown river rock, which means it fit through the 1/2" mesh screen when they separate the gravel into different products. So my gravel is 1/2" and smaller. It seems like fine media to me but I have a good population of composting worms. I think a mix between 1/2" and 3/4" would be even better but I've never found that size mix in an affordable option that wasn't limestone.

I personally think 1/4" and smaller may well give you some issues long term.

[William Sherman]

Frank,

Thanks for taking the time to respond; I did go to the Youtube video you suggested and found it quite interesting. After viewing that Youtube clip and going to his website and reviewing some more stuff, I have officially abandon my "pea gravel". I found a material which is purported to be washed river rock which they call landscaping mix. I'll see it tomorrow, but I was assured no clay and no limestone, and that it was 3/4" to 1" in diameter. Keeping my fingers crossed. With new water and gravel, hopefully I can get things to settle down and get some more fish. Thanks again.

Frank Gapinski said:

Hi William,
I hate to be a bearer of bad news but choosing gravel that is a quarter of an inch in size and smaller - all the way to fine sand grains is just asking for trouble. It looks nice at first. You think it should be ideal for Aquaponics but wait 6 to 12 months and you will have problems with your system.

The size of your gravel is just too small. You will slowly create anaerobic black zones where fresh oxygen will not be able to penetrate to oxygenate plant roots or microscopic bacteria. In fact anaerobic bacteria will colonize your system and other negative issues will arise.

Your dilemma reminds me of Murray Hallam's Aquaponics Secrets DVD trailer where Murray succinctly explains the very problem that you have shared with us all and how many people see his system and then reject his advice and do exactly what you have done. Choose gravel that they think plants will like....

See this link for a hint and an explanation of your problem:

http://www.youtube.com/watch?v=btUZBk8G1xk

You really need to get rid of your pea gravel.
Toss it out completely and get 20mm gravel or small pebbles about an inch in diameter.

I know this sound extraordinary but you need to create air pockets in your gravel grow bed system for oxygen to penetrate.
For worms to wriggle through...
For plant roots to penetrate and thrive...
Spaces for air pockets is crucial.
Hard to believe but this system that Murray has created will enable you to grow plants for over 4 years without cleaning the grow bed system and to it enable you to enjoy your Aquaponics journey with a trouble free system.

Cheers
Frank

[William Sherman]

TC,

Thanks for all of your help and advice. As I just told Frank, my days with "pea gravel" are over!!! I'm converting to "river rock" in the 3/4 to 1" size. Cleaning tanks and grow-beds is on tap for tomorrow, plus picking up the new gravel. Any advice to stabilize my system before I murder some more fish?

TCLynx said:

I guess I hadn't paid very close attention to size on the gravel. My gravel is 1/2" brown river rock, which means it fit through the 1/2" mesh screen when they separate the gravel into different products. So my gravel is 1/2" and smaller. It seems like fine media to me but I have a good population of composting worms. I think a mix between 1/2" and 3/4" would be even better but I've never found that size mix in an affordable option that wasn't limestone.

I personally think 1/4" and smaller may well give you some issues long term.