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Gravel and PH issues

Discussion in 'Water Chemistry' started by JasonW, Apr 29, 2014.

  1. JasonW

    JasonW Member

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    I just built several new large media beds and used some 3/4 inch river stone to fill them. I tested the stone and got one reaction from one of five containers filled with vinegar. It only bubbled for a few moments then stopped. Also did a ph test of the stone and although not completely neutral (mixed stone) it was not very high. I struggled with PH but have gotten it to hold now. Wondering if the initial bump in PH could have just been the sediment that did not get washed completely off the stone or should I expect to have more issues? Fought with the PH raising back up after using some Phosphoric acid but now after four days it seems to be holding. Thoughts?
     
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  2. Murray

    Murray Site Admin Staff Member

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    It is not uncommon to have pH swings while the system is cycling. Be patient. Seems like you are on the right track.
     
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  3. JasonW

    JasonW Member

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    I am just concerned that my stone has a base that is leaching and driving my ph up, which was 8.4 at one time. Im just unsure of when to become concerned with the stone and if I am just wasting my time with the media I chose. Any other tests that I could perform? I was told that if my stone is leaching I will never get rid of the problem until I switch media.
     
  4. Robert123

    Robert123 Active Member

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    Just keep record of pH versus time. Could well be that once the powdered rock is consumed, you may well be able to live with the minor pH instability that may still be present. It's normally a surface area effect and very predictable after an initial break in period. From what your saying, this sounds like your situation.
     
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  5. JasonW

    JasonW Member

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    I do have a great buffer , sitting about 14 gh and 12 kh so this is also posing a problem, I just have never had PH jump right back up over night after adding acid.
     
  6. Robert123

    Robert123 Active Member

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    Not sure I understand what the units of "gh" are?
     
  7. JasonW

    JasonW Member

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    GH of 12 is about 214 ppm and KH of 14 is about 250 ppm
     
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  8. Robert123

    Robert123 Active Member

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    Had to look that stuff up. I'm used to using pKa's and that method of describing a buffer is new to me. Interesting read.

    Was your water anywhere near that hard before it hit the grow bed? I guess you can monitor general hardness (GH) over time as well to determine if the rocks are continuing to dissolve. Maybe do water changes to keep GH in an acceptable range.

    Pretty Slick
    :thumbsup2:
     
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  9. Robert123

    Robert123 Active Member

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    P.S. I also like your choice to use phosphoric acid in this case as you should be more easily able to establish a sluggish pH response around 7 (i.e. make a phosphate buffer). Again, very smart :pompous:

    If you use phosphoric to drive your pH down to about 6.5, it will take a fair amount of base to lift it back over 7. Repeat as necessary ;)
     
    Last edited: Apr 30, 2014
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  10. Held

    Held New Member

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    i tried phosphoric acid once, ever since i have high phosphate readings. Can promote algae growth. My Ph was at 8.2 for a year, its finally slowly decreasing for the past 3 weeks or so, its sitting around 8 and dropping, give it some time. My Pepper plants don't show any problems.
     
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  11. JasonW

    JasonW Member

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    Thanks for the info! Robert my water is naturally that hard coming from my well.
     
  12. Robert123

    Robert123 Active Member

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    Good point on algae - especially if your tanks are getting a lot of sun. Shade will absolutely help if that is the case.
     
  13. Robert123

    Robert123 Active Member

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    Jason - You might want to consider collecting rain water and use that to replace (some of) the water in your aquaponics (not just use as top up water). That will help remove the carbonates that are buffering your pH up.

    (RO filters can be used to, but they cost $$)
     
  14. Held

    Held New Member

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    My well water is a little hard too, GH 160, KH 179, do to the rocks i used in my system, KH is high off the chart and my GH around 200, goldfish and kois are ok with it, some fish dont like hard water. I paintet my grow beds satin black and insulated my fish tank, i dont have much algae. i also have a Plecostomus in each fish tank to eat algae. my neighbor didn't paint the grow beds and now they are turning green.
     
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  15. JasonW

    JasonW Member

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    Robert, I have considered that but I think after things settle down with ph the hard water will help to keep my buffer up as nitric acid drives it down. Everything is well covered and algae has never been a problem in the past.
     
  16. Yabbies4me

    Yabbies4me Administrator Staff Member

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    The pH won't come down while you've got high carbonates Jason.

    Also, while you have high carbonates, adding acid directly into the main system will only create very short term pH bounces, as you've seen. This is why it's recommended you don't add acid directly into the system, rather treat any top-up water to a pH of 6.0 (and maintain it there) the day before adding it to the system, to consumes the carbonates.

    I wouldn't use Phosphoric acid as it can lead to algal blooms and high Phosphorus levels in the system, as has been mentioned. Instead use Hydrochloric acid, it disassociates into Hydrogen and Chloride, the Chloride is beneficial to fish health.
     
  17. JasonW

    JasonW Member

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    Yabbies, You are absolutely right and I always treat the water first then add it as you suggest, the carbonate levels I stated were what I started with and are now sufficiently lower and the PH has come down and stayed down. I was not aware though of the algae bloom problem and will go back to using HC acid from now on. Thank you for the great info.
     
  18. Robert123

    Robert123 Active Member

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    Phosphates are good for plants - and especially necessary to get good yields off of fruiting plants - but unfortunately algae is a plant so it's good for growing that too. Algal blooms can be devastating to an AP system very quickly as it can suffocate your fish before you get home from work on a bright, hot day. I have a high density of Tilapia, my nitrates are low and my tanks are shaded in the greenhouse so I have no issue with algae even on the sides of my tanks.

    What makes phosphate good for pH (and why your pH has stabilized around 7 now) is that it is tri-protic (there are 3 unique pKa's associated with each acid functionality). The 2nd acid releases about pH 6.5-7.0 and thus it makes a great mid-range buffer. You now essentially have two different buffers in your water. The phosphate at 6-5-7.0 and the carbonates (around pH 8 for the first carbonate proton - i.e. bicarbonate). Since you now have phosphate buffer in in there, switching to HCl will continue to utilize the phosphate as the pH 7 buffer till such time as the phosphate is consumed by the plants. Probably worth emphasizing again that shading is suggested even if your don't add more phosphoric for exactly the same reason (the phosphate is already in there). As Yabbies has indicated, adding more phosphate at this point will exacerbate any algal blooming issues should you have an environment ripe for it to occur. The P will eventually be consumed by your plants (albeit quite slow for vegetative plants like lettuce & other leafy greens) and may need to be replaced eventually if you want to keep that buffer in there, but it will be obvious when it's not in high enough concentration anymore to buffer pH since you also have carbonates in your system (you won't be able to hold neutral again and your system will want to run at pH 8). Perhaps nothing wrong with pH 8 depending on what fish/plants your are raising. I just like mine below 7 because of my high fish stocking density and fear of an ammonia spike if the biofilter goes down without me knowing it.

    I suggested collecting rain water, because you don't have a source of "clean" water. If you keep adding your ground water as top up water the carbonates will continue to increase. This can both overwhelm your neutral pH buffer and also it can cause fouling issues on equipment such as heater and/or pumps. Using rain water as top up water will not increase either the P or the carbonates in your system. If you periodically replace some of your AP water with rain water, you will start decreasing the content of both P and carbonate by simple dilution.

    P.S. - I have developed a habit of periodically exchanging some of my AP water (about 10%) each month just because I have no idea what else might be building up in the system that I might not want in there. As my system is small right now (only about 500 gallons) that is a luxury I can afford. When I expand later this year, I am seriously considering adding in a small RO unit.
     
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  19. Robert123

    Robert123 Active Member

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    Sorry for the run-on blather. Sometimes I get started and it just doesn't stop :yawn:
     
  20. JasonW

    JasonW Member

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    Thanks for all the info Robert.
     

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