Affect of pH on nutrients - Fertilizing - Aquatic Plant Central

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Old 04-10-2005, 08:36 PM   #1 (permalink)
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Default Affect of pH on nutrients

This is a post I made in another thread, but upon further consideration I think it warrants its own topic. Keep in mind I am no chemist or anything but it is something i have noticed. I also have noticed that pH seems more important in the "foreign" discussion groups but is rarely discussed here in the US. can anybody shed more light on this for me?

I have been wondering lately if some of these "problem" plants are responding poorly to the higher hardness or the higher pH. In 2 of my tanks, I was having alot of trouble with Ludwigia ovalis, Cuba and oddly Hemianthus micranthemoides. My hardness meant I injected CO2 to a pH of 6.7 for `35ppm Co2. After basically loosing all of the plants I decided to try lowering the pH to 6.4-6.5 within a week the L. Cuba was perking up and I had H. micranthemoides coming out of the substrate from complete non-existence. The L. ovalis was completely gone at this time. No other parameters changed as to my knowledge. I still have a Gh of 9 and a kH of 6 with an Eco/Onyx substrate. Interestingly, I allowed my pH to go back up in one of the tanks and the Cuba looks like crap again and the micranthemoides is not dieing but its not thriving much either.

Sorry I don't have much to offer regarding the Pantanal but I figure that info was still relevant. Does anybody know if/ how the lower pH would affect nutrient uptake, redox, availability or chelation?
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Old 04-10-2005, 10:19 PM   #2 (permalink)
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Hi dennis

The explanation must be quite complicated because rarely we see this issue discussed on hobby forums.
From my practical experience, lower the pH is healthier the plants are. I run some tanks at 0.25 dKH and pH of 5.0 and 4.0. Both look nice and clean. The plants love it. I also believe the TE are more available at those low pH levels. Secondly, lower light intensity is required to grow the same species. Not sure, if it is due to the low KH, pH, TDS or combination of all.

Anyone has the same experience?

Thank you
Edward
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Old 04-11-2005, 01:39 AM   #3 (permalink)
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Dennis, how do you lower ph to 6.4, just crank up CO2?

I have been wondering about the effect of ph as well, after reading Tsunami(Carlos)'s challenge to get bloodred L. 'pantanal' as some hobbiests in Asia are able to achieve with ADA stuff. They seem to claim softwater, low ph is important. With tap water, I was able to get pantanal quite red, but not NEARLY as red as I saw in asian forums. The closest I have seen in US was from Pineapple(AndrewCribb) with soft NYC water. I hope to setup an experimental tank in the near future, with peat to reduce ph and RO to controll hardness. Could it be that lower ph allows more effective uptake of Iron? Assuming iron is where most of the redness comes from.

Interesting thing is, those asian hobbiests say that ADA substrate loses most of its power after a year or two, and the Pantanal loses its redness. Then its time for them to re-do the tank. Sounds like that's due to Peat decomposition in ADA substrate? If ph of water is what matters, then putting peat in filter might be easier to replace.

By the way, 'cuba' is absolutely a weed for me at ph6.7-6.8, kh=4-5, gh=8-10. So are L ovalis and H. m.

Last edited by shalu; 04-11-2005 at 02:11 AM..
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Old 04-11-2005, 06:24 AM   #4 (permalink)
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Hi shalu

Peat can do only so much and it is not the best solution. It not only removes some elements but also adds some and that can make the final water with higher conductivity and immeasurable CO2 concentration. Not mentioning the instability due to peat filtration.
The issue here is KH. People in Asia enjoy tap water of almost RO parameters. Now thatís easy to work with.

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Old 04-11-2005, 10:50 AM   #5 (permalink)
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I know back in undergrad plant physiology that a protein found in the roots of terrestrial plants will cause the plants to take up more nutrients (I believe particularly iron) in the presence of low pH. I don't have the research articles with me but believe I saved them back in Austin. (I am not a plant physiologist, just took one course). I can only guess that aquatic plants undergo a similar mechanism?
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Old 04-11-2005, 11:30 AM   #6 (permalink)
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Quote:
Originally Posted by Edward
Hi shalu

Peat can do only so much and it is not the best solution. It not only removes some elements but also adds some and that can make the final water with higher conductivity and immeasurable CO2 concentration. Not mentioning the instability due to peat filtration.
The issue here is KH. People in Asia enjoy tap water of almost RO parameters. Now thatís easy to work with.

Edward
ok, I might just use RO without the peat. But I thought ADA substrate is peat based so I try to imitate that.
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Old 04-12-2005, 04:17 PM   #7 (permalink)
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Quote:
Originally Posted by shalu
Dennis, how do you lower ph to 6.4, just crank up CO2?


By the way, 'cuba' is absolutely a weed for me at ph6.7-6.8, kh=4-5, gh=8-10. So are L ovalis and H. m.
Yup, I just crank the CO2, which is controlled by a Milwaulkee controller. My Cuba is comming back, guess it did not like being moved around.

I know that the pH of soil will affect nutrient uptake and availibility in terrestrial plants, I do not know either how/if it works in submersed aquatic plants. Logic tells me that a low pH is more acidic, therefor the water would dissolve minerals like Ca, CO3, Mg etc faster making them more available to plants. Lower pH seems to have some kind of algae inhibiting affect. Doesn't the addition of mulm and peat to the substrate create an acidic enviroment? I thouhgt that the organics not only sofen the water by stripping the carbonates but their decomposition forms an acid, right? If memory serves, does an acid environment breakdown the bonds between compounds, like FePO4, and chelators, thus making the nutrients more available to plants? Also, I thought the good bacteria preffered slightly acidic conditions, I am talking stuff that lives in the substrate.

Somewhere I think I have seen info stating that lower pH helps the plants to take up and utilize nutrients but I do not remember where.....
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Old 04-12-2005, 05:10 PM   #8 (permalink)
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Dennis,

I am curious on the effect of the low pH on your fish? Not from the pH point of view, but from the amount of CO2 you must have in your system? I have raised my co2 levels accidentally to the mid fifties with no short term effects on my fish, but would be concerned about going on for too long. Do you see them gulping at the surface?
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Old 04-12-2005, 06:55 PM   #9 (permalink)
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Before moving from Maryland, I kept my Co2 levels in the 50ppm range. The only effect I noticed on my fish was that the German Blue Rams started spawning. Not sure if this was just a coincidence or if it was triggered by the lower pH. The Cardinals didn't seem to mind and neither did the Amano or Cherry Red Shrimp.

I must also add that, at the time, I used AP test kits for KH and pH. Not sure how reliable these test kits are.

I don't see a problem in cranking up the CO2 as long as the fish aren't stressed.
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Old 04-14-2005, 05:16 PM   #10 (permalink)
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Bert, I have not noticed any ill effect on either the fish or Amano shrimps

I have been doing some research via Google Scholar and through the basic college Bio/chemistry text books. This is what I have found so far. Keep in mind I am just assimilating and regurgitating the info. Also, most of the info out there pertains to soil and terrestrial plants.....

Basically minerals/nutrients are either positively + or negatively - charged. Elements like K+, Ca+ and Mg+ and Fe are all positively charged while NO3-, H2PO4-(phosphate) and SO4(-2) are negatively charged. Opposites attract here in that positive minerals tend to adhere via electrical attraction to negatively charge clay particle in the soil. This is the reason why Flourite and Power Sand(I think) work so well long term. They collect nutrients into the substrate. Negative charged minerals/ nutrients tend to not bind to anything and are washed away easily. This is why soaking soil is recommended and why NO3/PO4 are most necessary in the water column.

How does pH affect this?......
pH is basically a measure of whether something is an acid or base. Acids tend to liberate hydrogen(H+) ions while base solutions liberate hydronium (OH) ions. Acidic water is preferred by plants because the H+ ions bind with minerals attached to the clay particles through cation exchange. Plants roots are designed to use and move H+ ions. Plants often release H+ into the soil to break down nutrient bonds. Plants also use the H+ to allow negative solute, like NO3- to enter the cells through "carriers" that only work if they can take up H+ at the same time. This is called cotransport and functions through chemiosmosis (remember that osmosis is the process by which something is drawn through a membrane based on pressure and particulate solution) H+ also helps move compounds like sucrose throughout the plant. Also, stomatal openings (the tiny "holes" in the surface of leaves, stems and roots that let things in and out the plant) are also affected by the transport of H+ throughout the plant.

Basically, H+ is necessary for most of the functions and nutrient use of the plant. And we wonder why pH seems to play a factor!

Hopefully those of you who are more versed in this subject can shed more light and correct any misinformation I may have provided
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