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Low pH - Using shell grit to counter low water pH

Discussion in 'Water Chemistry' started by Yabbies4me, Dec 22, 2013.

  1. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Using Shell Grit to Control Low pH

    A few days ago the pH in our IBC display system started dropping and I started adding small amounts of Hydrated Lime and Potassium bicarbonate, alternating every day. I was managing to get the pH up from 6.0 to 6.3-6.4 each day, but yesterday morning it had plummeted from 6.3 to 5.5 overnight.

    So to kill two birds with one stone I did a tank clean with a siphon hose and replaced the 60L or so of water lost during the clean with aged tap water which has a pH of 8.4, this brought the system pH back up to 6.0

    Over the course of the day I also added a small amount each of Hydrated Lime and Pot’ bicarb, this brought the pH up to 6.4 by yesterday afternoon, but before leaving the shop in the evening I did a pH test and it had started to drop already, it was sitting 2 points lower at 6.2... This is when I decided to experiment with the effectiveness of shell grit as a pH buffer. I've used lumps of limestone before on numerous occasions in other systems, but never the shell grit... so I went and bought a small bag from the bird shop nearby.

    I incorporated 4 handfuls of the shell grit into the grow bed by digging down to below the max’ fill water level and adding the shell grit, working it into the gravel, then recovered the holes with the expanded clay.

    I expected the shell grit to take a few days to start having any effect, but his morning I tested the system pH and was amazed to find it had hardly moved overnight. It had only dropped from 6.2 down to 6.1... I have just tested again a little while ago (early evening here now) and it’s still sitting at 6.1... So not only did the shell grit dramatically slow the pH drop within hours of going into the system, but it appears that it has completely arrested the pH decline with 24hrs of going in. I will keep posting the results over the next few days for those interested in this experiment.

    Cheers!
     

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  2. Gratilla

    Gratilla Member

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    Do you know what's causing the acidity?
     
  3. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Yep, just the Nitrification.

    The Trout I pulled out of the system a bit over a month back were slightly overstocked (10% above recommended), as an experiment I knew I could get away with over winter. As the fish matured towards the end of the season the Nitrification that went on in the system was phenomenal, my pH would go from 6.3-6.4 down to 5.5-5.8 every single day. I was constantly doing partial water changes, to not only clean out the fish waste from the FT, but also just so I could add some of our high carbonate water. I was also adding Hydrated lime and Potassium bicarbonate on a daily basis. For the last month or so it was a constant, daily battle due to the high amount of Nitrification going on... which obviously stripped the water of any carbonates and pH buffering ability.

    After the Trout came out I did a few more partial water changes over the couple of weeks the system was empty, just to add some carbonates, primarily to bring the water pH back up into mid 7's, so it closely matched the water the new batch of SP's would be coming from, and secondly to get some pH buffering capacity back in the system.

    When the SP's went into the system (stocked at sensible rate this time, no overstocking experiments over summer) about a month ago, it didn't take long for the pH to begin dropping, very slowly at first, but this accelerated over the last week, then one day just plummeted, even with hydrated lime and Pot' bicarb added the night before... obviously the carbonates have been exhausted. So while the water top-ups I did to bring the system pH up to the mid 7's before adding the SP's, did add some carbonates, it obviously was nowhere near as much as was in the system initially, because the Trout took a lot longer to remove the carbonates from the water and they were larger than the SP's when they went in and also fed at a much greater rate.

    Long story short Gratilla, Nitrification going on and carbonates in the water exhausted... So rather than having to add either Hydrated lime or Pot' bicarb everyday and also to avoid the corresponding pH bounce, I need a constant source of carbonates being steadily released into the system.

    Cheers.
     
  4. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Update:

    As reported at the start of this thread, the pH only dropped 0.1 in the first 16hrs after adding the shell grit, whereas the day prior it had dropped 0.8 in less than 24hrs. I retested 24hrs after adding the shell grit and the pH was still only down the same 0.1... so it looked like it had not only slowed, but arrested the pH decline... or so I thought.

    Today is three days since the shell grit was added and when I tested this morning the pH had dropped a little further, from 6.1 down to 5.9 (pic 1.)... so it's still declining, just at a greatly reduced rate.

    I believe the reason for the outstanding results in the first 24hrs may have been due to there being a lot of very fine particles, basically shell dust, in the four handfuls I added to the GB and these would've had an almost immediate effect on controlling the pH decline, then once they were consumed by the natural acids in the system the pH was able to start declining again, albeit at a much reduced rate.

    I think the larger particles of shell grit will take a few days to start having an effect on the pH in the system, then hopefully we should see it actually start to climb. In the meantime I've added a small amount of Potassium bicarbonate to arrest the decline, just until the shell grit begins working. This addition of Pot' bicarb brought the pH up from 5.9 to 6.2 (pic 2.)

    Pic 1 - Perth Aquaponics - pH 3 days after adding shell grit.jpg Pic 2 - Perth Aquaponics - pH 3 days after adding shell grit.JPG
     
  5. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Update to Shell Grit Trial

    Background:


    Prior to adding the shell grit the system pH was plummeting from low 6's down to mid-high 5's everyday, requiring daily additions of Potassium bicarbonate and/or Calcium hydroxide to keep raising the pH.

    The shell grit was added, starting in December, with 4 handfuls buried in the gravel grow bed, followed a few weeks later by 6 handfuls suspended in a stocking in the FT.

    After both additions the pH either stabilised temporarily, or the rate of pH decline slowed substantially. However, after only a few days the pH would again start declining everyday, just at a slower rate than without the shell grit. The Potassium bicarbonate or Calcium hydroxide were only required about every third day.

    In the last couple of weeks the pH decline had increased again, to the point where buffering was required almost daily, even with the stocking of shell grit still suspended in the fish tank, so I decided to try adding a few pieces of clean limestone for comparison sake.

    I've used limestone with outstanding success in the past, but was informed by a number of other experienced aquaponics practitioners that I should be using shell grit, as it worked better, or so they claimed.

    Limestone added:

    On Friday 21/3 I located some clean pieces of limestone (pic.1). As I was unsure of their past history I soaked them in a bucket of warm water to remove any possible toxic substances, such as oils, weedkiller etc (pic.2).

    Four small pieces, each roughly the size of a sardine tin, were added to the fish tank of the IBC display system on the afternoon of the 21/3 (pic.3). The pH of the water prior to adding them was 6.2 (pic.4).

    The pH was tested 24hrs later and a pH reading of 6.5 was recorded, a rise of 0.3 (pic.5).

    The pH was tested again today, 3 days after adding the limestone, and as can be seen from the picture (pic.6), it is sitting on 6.9... a rise in pH of 0.7 in just three days.

    I will keep tracking the pH over time, but at this point I think this demonstrates the effectiveness of limestone over shell grit for raising/buffering pH.
    ...
    Perth Aquaponics - Limestone 21-3-14 - Copy.jpg Perth Aquaponics - Limestome soaking 21-3-14 - Copy.jpg Perth Aquaponics - Limestone added 21-3-14 - Copy.jpg Perth Aquaponics - pH Test 21-3-14 - Copy.jpg Perth Aquaponics - pH Test 22-3-14 - Copy.jpg Perth Aquaponics - pH Test 24-3-14 - Copy.jpg
     
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  6. silloth52

    silloth52 Member

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    thanks for the info yabbies, having the same problem chasing my ph virtually everyday
    will try and source some limestone and give it a go
     
  7. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Over the last couple of years that I've been running the limestone in the system I've found it reacts much in the same way as the shell grit, in that the pH rises initially due to the acids in the water having easy access to the carbonates on the outside of the limestone blocks, especially the fine, loose particles that are easily dissolved, but then the pH stabilises and begins to decline again. The process is just slower with the limestone as opposed the shell grit.

    I've found that every few weeks have to rub the flat surfaces of the limestone blocks together to remove some of the biofilm from the surfaces, which I believe restricts the ability of the acids in the water to access the carbonates within the block. Once rubbed together there is an immediate increase of a few pH points, but within a day or two the pH decline begins again.

    As suggested by someone on my FB page recently, the efficiency of the limestone could probably be improved by crushing the half dozen small limestone blocks into many more even smaller chunks, but in my situation this would inhibit me from being able to properly siphon/vacuum clean the floor of the FT, which I do once a week.
     
  8. Terra

    Terra Active Member

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    At my previous property I used limestone in my sumps (easy access) to steady the ph decline .

    I used large rocks every week I would crack some in half and put back in worked well , yes the bio film interferes with buffering the cracked rocks provide new surface .

    I get good results from dolomite this seems to last awhile , however I don't know the calcium / magnesium ratio so im basically winging it .

    Maybe a small container run constant flood that we can adjust the flow rate full of lime gravel that's easy to tip out and replace could work for us just adjust the water flow rate this might be the best option on the smaller systems that can move quickly

    Its interesting the people with high Ph battles due to their media , struggle with this for ages however putting limestones in growbeds makes little difference for me .

    Ive tried digging big holes in the corner of a growbed putting a large garden pot in and filling with lime gravel , putting mid size rocks in corners (so I can find them).

    Best results have been the large rocks cracked each week as its easy to manage

    Aquaponics is great brain exercise if nothing else
     
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