low ph a norm in new tank? - The Planted Tank Forum
 
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post #1 of 11 (permalink) Old 01-16-2007, 01:31 AM Thread Starter
 
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low ph a norm in new tank?

Hey everyone,

First off i want to thank everyone for all the indirect help i've had in starting my planted 10g tank. I think that with your help I've really avoided mistakes I probably wouldve made if not.
The tap water in my house is generally soft but close to neutral. My tank had been giving ph readings of around 6.8, but lately has decreased to around 6.4. My tank is in its first week of cycling with a betta and lots of wendti crypts, an amazon sword, java moss, anubia nana, and alittle bit of java fern. I run 2 x 15 watt incandescents on a standard hood for 8 hours a day, although im looking to upgrade to the Coralife 20' 1 x 36.

My question is, is the ph dropping because of new bacteria forming? Or could there be another reason i should be aware of. I was doing 30% water changes every other day, but I'm now going to start doing them once a week.

Thanks to everyone in advance,

julio
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post #2 of 11 (permalink) Old 01-16-2007, 03:21 AM
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A pH drop from 6.8 to 6.4 isn't a problem for plants or fish, since it occurs pretty slowly. It could be from the plants using carbonates for a carbon source. Not many plants can do that, and I'm not sure those you have can do it, but that would drop the pH along with the KH. If you have a piece of wood in the tank for decoration, leached tannins from the wood will also drop the pH and give a yellowish color to the water. If you have peat in the substrate, that can drop the pH if the peat isn't completely buried under the substrate. If you are injecting CO2, that, of course, drops the pH too. And, last, if your tap water is unusual in not having any dissolved CO2 in it, your soft water may be low in KH too, so tank water absorbing atmospheric CO2 will drop the pH.

Hoppy
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post #3 of 11 (permalink) Old 01-16-2007, 03:52 AM Thread Starter
 
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thanks for the help

their is no co2 in the tank yet, although im thinking of getting a DIY after getting the light. The wood has released some tannins into the water, keeping it consistently yellowish. I think its slowing down though, and hopefully after my next water change it'll get back to normal.
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post #4 of 11 (permalink) Old 01-17-2007, 03:48 AM
 
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Ph Dropping

I beleive the buffering capacity (kh) is going down slowly, by doing so your ph is going down to.

1— the water you used for water change have already a low kh reading.
(I guess around +- 20 mg/l or ppm)


2— The establishment of the biological filter (nitrification) is another consumer of carbonates that lower your kh

Quote:
A reduction of total alkalinity may accompany nitrification because a significant amount of bicarbonate is consumed in the conversion of ammonia to nitrite. A model developed by Gujer and Jenkins (1974) indicates that 8.64 mg/L of bicarbonate (HCO3-) will be utilized for each
mg/L of ammonia-nitrogen oxidized. Reductions in alkalinity can cause reductions in buffering capacity, which can impact pH stability.
the range of ph between 6.5 to 7 is where the plants can have a better consomption of nutrient.

Lower ph will slow down the nitrifying process (bacteria responsable for the process prefer a ph around 7), slowing down the carbonates used.

You can add a small amount of CaCo3 to raise your ph and help to ”feed” those bacteria...
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post #5 of 11 (permalink) Old 01-17-2007, 11:12 PM Thread Starter
 
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Originally Posted by Glouglou View Post

You can add a small amount of CaCo3 to raise your ph and help to ”feed” those bacteria...
any idea how much i would have to add to slowly raise the ph? thanks for the replies
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post #6 of 11 (permalink) Old 01-18-2007, 12:05 AM
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Quote:
Originally Posted by Glouglou View Post
I beleive the buffering capacity (kh) is going down slowly, by doing so your ph is going down to.

1— the water you used for water change have already a low kh reading.
(I guess around +- 20 mg/l or ppm)


2— The establishment of the biological filter (nitrification) is another consumer of carbonates that lower your kh



the range of ph between 6.5 to 7 is where the plants can have a better consomption of nutrient.

Lower ph will slow down the nitrifying process (bacteria responsable for the process prefer a ph around 7), slowing down the carbonates used.

You can add a small amount of CaCo3 to raise your ph and help to ”feed” those bacteria...

But this is a planted tank. Low pH is nothing to worry about. 6.4 is fine. I would not mess with calcium carbonate unless you have fish that like hard water. Most plants will do better at lower kH's.


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post #7 of 11 (permalink) Old 01-19-2007, 02:56 AM
 
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CaCo3

You can go to your aquarium supply where you can look for some KH booster (must of the time it is CaCO3) go with the instruction.

You can find baking soda anywhere

To raise both GH and KH simultaneously, add calcium carbonate (CaCO3). 1/2 teaspoon per 100 liters of water will increase both the KH and GH by about 1-2 dH. Alternatively, add some sea shells, coral, limestone, marble chips, etc. to your filter.

To raise the KH without raising the GH, add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.


This is for ianiwane, I agree that 6.4 is still OK for plant, but some nutrients absorption in plants start to decrease around 6.5. This is the case for (phosphorus, calcium, magnesium, molybden)

The only nutrient absorption rate that is actually help by lower PH than 6.5 is Iron passing from around 88% absorption rate to 100% absorption rate at 6.
You have no advantages to go lower than that only in very specific situation

At ph 6, phosphorus absorption is only around 25% to go up to around 98 % at ph 6.5

Last edited by Glouglou; 01-19-2007 at 03:02 AM. Reason: mistake
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post #8 of 11 (permalink) Old 01-19-2007, 04:26 AM
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That is all well and good but does it all really matter, my pH is about 6.0-6.2 in my tanks. Take a look at my signature, the plants grow really well. Can I have some reference links to studies done that show absorbtion rates? It is well known from many peoples experiences that many plants grow better in low pH's and kH's. In practical experience how does it work.


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post #9 of 11 (permalink) Old 01-19-2007, 05:14 AM
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Also one more thing to add, certain plants do not like changes in kH or gH. One to be noted is downoi. Downoi tends to melt easily when the water hardness is changed.


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post #10 of 11 (permalink) Old 01-19-2007, 06:07 AM
 
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Quote:
Originally Posted by Glouglou View Post
You can go to your aquarium supply where you can look for some KH booster (must of the time it is CaCO3) go with the instruction.

You can find baking soda anywhere

To raise both GH and KH simultaneously, add calcium carbonate (CaCO3). 1/2 teaspoon per 100 liters of water will increase both the KH and GH by about 1-2 dH. Alternatively, add some sea shells, coral, limestone, marble chips, etc. to your filter.

To raise the KH without raising the GH, add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.


This is for ianiwane, I agree that 6.4 is still OK for plant, but some nutrients absorption in plants start to decrease around 6.5. This is the case for (phosphorus, calcium, magnesium, molybden)

The only nutrient absorption rate that is actually help by lower PH than 6.5 is Iron passing from around 88% absorption rate to 100% absorption rate at 6.
You have no advantages to go lower than that only in very specific situation

At ph 6, phosphorus absorption is only around 25% to go up to around 98 % at ph 6.5
6.4 just 'OK'??? Seems the discussion here lately was that really low KH and ph values going down into the 5's were great for plants, atleast on heavily planted co2 injected tanks. I have stopped dosing bicarb once I read these low KH discussions.
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post #11 of 11 (permalink) Old 01-19-2007, 04:02 PM
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Quote:
Originally Posted by Glouglou View Post
but some nutrients absorption in plants start to decrease around 6.5. This is the case for (phosphorus, calcium, magnesium, molybden)

The only nutrient absorption rate that is actually help by lower PH than 6.5 is Iron passing from around 88% absorption rate to 100% absorption rate at 6.
You have no advantages to go lower than that only in very specific situation

At ph 6, phosphorus absorption is only around 25% to go up to around 98 % at ph 6.5
Glouglou;

Are these absorption rates you quoted from studies with terrestrial plants with absorption from their roots? Or are these rates actually submerged aquatic plants with nutrients in the water column and absorption from leaf tissue? I'm just wondering is this happening in our underwater aquatic systems when using EI fertilization and injected CO2 - which does tend to drive our PH lower?
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