How do you control your pH

scott_dc

I've seen lots of bunk and discussions from people that obviously don't know much about water chemistry (but claim to). While I don't know much about fish or plants except what I've read here, I have experience in inorganic water chemistry so thought I'd contribute some knowledge.

This is what I do and why. Feel free to do something different or disagree.

I use rainwater. I think the same method would work with hard water that was treated with hydrochloric acid (muriatic) to neutralize pH but I haven't done this personally.

Here goes:

1) CABONATES DO NOT BUFFER pH IN THE RANGE OF INTEREST TO AQUAPONICS. If your pH is stuck above 8.2 or so, then carbonates are to blame. If your pH is below that (say, 7), any carbonates will form an equilibrium between bicarbonate and dissolved carbon dioxide. The carbon dioxide will be in equilibrium with the atmosphere. Any excess carbonate/bicarbonate will form carbon dioxide and be released to the atmosphere. Some of these reactions can be slow (days), which can be good or bad, but this is not buffering.

2) The only effective buffer I have seen that is good for plants and fish is phosphate. Some organics might work but they or their breakdown products would probably be bad for fish or plants. Phosphate is a very effective buffer right in the pH range ideal for aquaponics. I try to maintain about 50-100 ppm phosphate in my system by occasionally dosing with mono-potassium phosphate (mkp). It doesn't take much and the phosphate doesn't get used very quickly. I measure it with the API phosphate kit (works to 10ppm so I have to dilute to measure). I've seen lots of posts that say to avoid too much phosphate because of algae blooms. However, I keep my fish tank shaded and have had no problems with algae. I can understand why phosphate is bad for aquariums and ponds (exposed to light) but I want my water to be conducive to good plant growth--that's the whole point.

3) The nitrification process decrease pH over time. This requires periodic adjustment to maintain pH in a good range. I don't think there's any debate on this point. Part of me thinks that plant roots put out chemicals that decrease pH too. That's how they get nutrients like Fe from the soil (or so I've read).

4) I previously added potassium hydroxide and calcium hydroxide to keep pH up. I did this because of various posts/threads that said carbonates are bad because they buffer pH too high. The phosphate noticeably decreased the frequency of adjustments and allowed me to add more each time without dramatic pH swings. This is the point of a why I added the buffer (phosphate). However, pH did still swing up with each addition and drift down over time.

5) Realizing the chemistry noted in paragraph 1), above, I put in a mesh bag of egg shells, which are calcium carbonate. If completely dissolved, they would increase pH too much. However, they only slowly dissolve. Higher pH makes them dissolve more slowly and lower pH more quickly. This is just what I want. I keep the bag in the water. If the pH starts to creep too high, I take the bag out. Too low, put the bag in. Other forms of calcium or magnesium carbonate would work (limestones, oyster shell, probably any growbed media that fails the vinegar test). Note, i don't crush the shells because I want them to dissolve slowly.

6) With the combination of the phosphates buffering the pH (paragraph (2)), and the egg shells slowly dissolving, my Ph remains rock steady for weeks on end. THe bag stays in for several weeks, then come out for a week or so. No pH swings, pH always in a good place.

7) I dose with maxicrop and potassium nitrate as needed to keep K in line with Ca. Some have suggested that I may have a Mg issue so a dolomitic lime might be a good option instead of the egg shells. I also occasionally dose with very small amount of epsom salt but I don't like to because I can't measure Mg or sulfate and I don't want it to build up.

please let us know how you control your chemistry and/or how I can make mine better.

scotty435

I'll agree with what you've said. I'm probably one of the culprits, I tend to think of buffers as systems, not their effective range and when they are actually functioning to stabilize the pH within a certain range. With that in mind Phosphate buffers are the only ones that really are working to stabilize the pH within the 6 to 7 pH range (at least that I know of). As you've noted however since the nitrification process is pushing the system toward the acid side and the dissolution of CaCO3 in egg shells is acting to reverse this trend :dontknow:

The Calcium carbonate isn't slowing the pH change like it would within it's buffering range but it is still slowing the effect of the acids generated by nitrification.

As long as you're covering your tank the phosphates won't likely cause an algae bloom. A UV sterilizer is another option, this is what I use in my Recirculating Aquaculture System. Most AP systems contain phosphates although it's difficult to be sure what form they are in. I think these eventually get bound up in organic compounds and are no longer readily available to the plants - at least this is why I think systems initially have algae and go through the pea soup phase and then wind up no longer having algae problems, even if they aren't covered. Having said this I realize that good amounts of phosphates can be found in fish food as well so there may be another reason but I know if I add phosphates the algae is back.

The method I use to stabilize my pH is very much like yours (shell grit or crushed coral in a bag) only I don't generally add MKP and my pH is reasonably stable without it. I don't worry about adding carbonates to the system and periodically add potassium bicarbonate if the pH needs a boost up. My system pH would likely be more stable using MKP but it's pretty stable without, there's very little algae and the tank is exposed. I usually show phosphate readings of 0 to 3 ppm but I believe the kit isn't detecting all the phosphates that are present.

Rather than dosing with epsom salts in the water, apply it as a spray and the same with the Maxicrop. You have to be a bit careful about what time of day with this since epsom salts can burn the foliage (I think I have the amounts around here if you need them). I'm not sure about the potassium nitrate additions since I seem to get enough potassium using Maxicrop plus iron but may have some coming from other sources that I don't know about (like the media or the water).

Dolomite lime might be a good option just look to see if it has lots of heavy metals or other components that you don't want in a recirculating system. It's occasional use for the magnesium is a bit different than leaving it in the system most of the time (at least in my mind :dontknow:

)

Note: I believe that at one point Andreas (DasBoot) was using MKP (not sure if he still is) but I believe he was spray applying it for deficiencies - I'm not sure if it is relevant in any way to this discussion but thought it might be of interest to you.

One other note - I'm not certain where the KOH/CaOH method was born but I know there is a video explaining it on YouTube if you search for Nate Storey and pH adjustment you'll probably get it. I look at it as just another method, each has advantages and disadvantages and I'd just go with whatever you are comfortable with or is easiest and works :thumbright:

Cheers

Charlie

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scott_dc

Thanks for the info on dolomite. I hadn't considered heavy metal buildup. I won't pursue that as an option. One other thought that I had was to use a calcium/magnesium dietary supplement or antacid tablets, which are mostly calcium carbonate and magnesium oxide or hydroxide. THis would be more expensive than the (free) eggshells I use now.

I'm a little irrationally afraid of foliar spray. THe one time I tried, I nearly killed all the plants by burning most of the leaves. In hindsight, I think it was a combination of tender plants (lettuce) and I sprayed on a hot sunny day but the memory of seeing a bunch of brown wilted plants remains etched in my mind.

It was Dr. Storey's video that lead me to the KOH/CaOH route. Now that I have experience, I would never recommend using KOH. It can be dangerous and can cause very high pH swings and has almost no advantages over KCO3 for an AP application. Making a concentrated KOH solution can cause serious injury and adding too much KOH at once can kill everything in your system. KCO3 is just as effective (on a molar basis) and is much safer to use and handle.

scotty435

I think you may have misunderstood what I was trying to say with the dolomite - I just wanted to be certain you looked at the heavy metals. I wasn't trying to say that the heavy metals were necessarily a problem in dolomite and products will vary. You'll find that most fertilizers and chemicals have traces of heavy metals. Washington, Oregon and California keep databases with this information listed by supplier or product. Here's the start of the Washington State one - http://agr.wa.gov/PestFert/Fertilizers/ProductDatabase.aspx. I think it's just good practice to limit these as much as possible. Sometimes I do this by using a brand with a lower amount per dose or using fewer doses, whatever works.

If I remember right, his goal was to keep the carbonates to a minimum to control his pH more easily, it's pretty understandable why he didn't use the KCO3. If you're starting out with really hard water then I think the use of KOH and CaOH makes more sense because you won't be adding to the carbonate hardness. The arguments for and against things like this have a lot to do with how and what you are trying to grow. The other thing that many try for using this is a balance of potassium and calcium (magnesium is also important since they compete for intake). I don't think the exact ratio of these is particularly important just that they both are present in adequate amounts.

Tough break on the foliar feeding but if you do it right and using the right dilution that kind of thing almost never happens.

scott_dc

Regarding dolomite. Undertood. Thank you.

Regarding KHCO3, if a system is at pH around 7 or below, carbonates aren't an issue (see my paragraph 1, in the first post above). If adjusting pH up, the bicarbonate will turn into carbon dioxide. If KHCO3 is over-added, your pH could get buffered above 8. However, the alternative, KOH, if over added could cause very high pH and certain death.

Judester

Good discussion thanks for the thread

Perfect timing for me too :thumbright:

I have, to date, used a large Limestone rock in my ST to manage my PH. It has worked a treat for 18 months.
No Ph adjustments required in that time. I have used this approach in my KOI ponds for years with no issues- but no plants in those ponds

However in the AP system
Plant growth did come to a full stop in the last few months, so more investigating lead to the Nate vids mentioned above.

The problem with my approach (5kg + of limestone approx 6000L water in AP system) in the ST reduces or prevents other plant needs (which are also + ions) such as Mg+ and K+ from being absorbed = no growth

I assume my TDS reading of 585 is indicative of this issue

I have just planned for a change in the way I manage my system to reflect what Nate has suggested

[*]KOH to supplement K+ needs when Ph is acidic
[*]Kelp solution if Ph stable and K+ required
[*]Mg+ periodically
[*]FeDTPA periodically
[*]Smaller volume of limestone or shell grit to manage TDS to around 200 (Nate has suggested under 200 is the goal.)

After removing all the Limestone 3 weeks ago the TDS has dropped to 500

Can anyone suggest a way of reducing the TDS count a little faster without massive water changes.
I top up with a bore which has a TDS of 300 so wont make that much difference.
Or can anyone see a problem with my approach?

Cheers

Gunagulla

Maybe just top up with rainwater for a while.

Judester

Good discussion thanks for the thread

Perfect timing for me too :thumbright:

I have, to date, used a large Limestone rock in my ST to manage my PH. It has worked a treat for 18 months.
No Ph adjustments required in that time. I have used this approach in my KOI ponds for years with no issues- but no plants in those ponds

However in the AP system
Plant growth did come to a full stop in the last few months, so more investigating lead to the Nate vids mentioned above.

The problem with my approach (5kg + of limestone approx 6000L water in AP system) in the ST reduces or prevents other plant needs (which are also + ions) such as Mg+ and K+ from being absorbed = no growth

I assume my TDS reading of 585 is indicative of this issue

I have just planned for a change in the way I manage my system to reflect what Nate has suggested

[*]KOH to supplement K+ needs when Ph is acidic
[*]Kelp solution if Ph stable and K+ required
[*]Mg+ periodically
[*]FeDTPA periodically
[*]Smaller volume of limestone or shell grit to manage TDS to around 200 (Nate has suggested under 200 is the goal.)

After removing all the Limestone 3 weeks ago the TDS has dropped to 500

Can anyone suggest a way of reducing the TDS count a little faster without massive water changes.
I top up with a bore which has a TDS of 300 so wont make that much difference.
Or can anyone see a problem with my approach?

Cheers

scott_dc

What is your ph? Other water parameters?

I don't think 500 ppm tds would necessarily be a problem. I have been running at 1000 for a while because I added salt for ich.

Use potassium bicarbonate instead of KOH.

scotty435

+1 to Gordon and Scott's comments. Use some caution on where you take rainwater from, it's not always a good idea to use it.

I would spray apply everything but the potassium bicarbonate (it looks like this might be your intent but it's been awhile since I looked at Nate's videos). For the seaweed extract I'd spray fairly early in the day. For something like Epsom salts (Magnesium sulfate), I'd spray a little before dark. Try it out on a plant if you're not sure since it is possible to burn the foliage.

Once you have the nutrients more balanced, adding more plants should also help with the TDS.

Judester

Hi Scott_dc

Ph sits at 6.4
Nitrates plenty
Fe 1 to 1.5

I dont measure anything else

Your TDS at 1000 really puts a new spin on things for me. I really liked the Limestone block approach to managing Ph, it was so simple

I am no expert but salt would I assume increase total dissolved solids and not have the same affect as the CaCO3. In my case the high TDS is dissolved limestone which is competing with the uptake of K and Mg.
So a high TDS may not be detrimental pending the underlying cause... as I said no expert

Scotty435
I was intending to add the additional nutrients to the water not foliage spray
I do have kelp solution which I could apply foliarly though. but maybe that will bypass the issue I have with TDS in solution?

Cheers J

scotty435

Judester wrote:

I do have kelp solution which I could apply foliarly though. but maybe that will bypass the issue I have with TDS in solution?

It will bypass the issue but the levels of potassium are probably only around 1 or 2 % in the kelp solution so I think this in combination with using the potassium compound of your choice to raise the pH of the system water makes more sense.

maxhill

Excellent post. Thanks.

It never occurred to me to dilute the test sample. So it my test requires 5ml test sample , and I double it to 10 ml keeping the reagents amount stable , I should double the resulting value of the colour matching chart?

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scott_dc

For my 5 ml sample, I add 1 ml of my system water and 4 ml of rainwater or distilled water. I then multiply the results by 5. Or, 1 ml of system water, 9 ml of rainwater, mix, use 5 ml of the resulting mixture for test and multiply results by 10.

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