KH and GH dropping (NPT) - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 10-10-2009, 08:15 PM Thread Starter
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KH and GH dropping (NPT)

Hi folks,

I have a large 200 Gal set up with regular potting soil, lighting is 128W of T8 (+ good sunlight). No CO2.

My tap water comes out at KH 7, GH 12 and pH 7.
Tank water is KH 5, GH 8 and pH 8 (i tested both today and 1 week ago).

Seems like my tank is consuming hardness too fast. It's been running for only 3 weeks, and since i'm not supposed to make much WCs with an NPT, i'm thinking that after a few months w/o a water change i'll be left with no hardness at all.

What is going on?? is this tendency (to drop hardness) is common in newly set ups, or am i running into a problem?? Perhaps there is too much light/not enough CO2 making the plants (and algae!) deplete the carbonates and minerals in the water?

It's got lots of simple plants:
Ceratophyllum submersum, Anubias, Echinodorus ‘Rose’, Egeria densa, HC, Hydrocotyle verticillata, Hygrophila difformis, Bacopa caroliniana, Vallisneria americana and a couple unidentified plants that look like green Ludwigia....

Thanks in advance!
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post #2 of 8 (permalink) Old 10-10-2009, 11:23 PM
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The tap water may have more than room equilibrium CO2 in it, and that would explain the rising pH. The GH drop seems to be more than I would expect, but plants do use calcium and magnesium - not that much in such a short time, with low growth rate though. The KH drop could be from the vals using up carbonates, assuming they are growing as fast as that species of val is known to do. You can start dosing with Seachem Equilibrium or other GH booster to keep the GH up, and use some crushed coral in the filter to slow down the drop in KH. Just some thoughts - not real advice.

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post #3 of 8 (permalink) Old 10-11-2009, 02:33 AM
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Test your tap after letting a filled container (glass/cup, etc.) set open overnight regarding the the pH reading. This allows the water to out gas what ever it contains from running through the pipes.
On a new NPT with potting soil the substrate should be gassing if the soil contains organics (which it should) so a rising pH tested result is odd. After submerged the soil should start discharging natural CO2 as bacteria starts munching the organics. My Walstad style tank gassed for approx. 5 months giving me free CO2 (it started testing a decreased pH level after two weeks submerged) I've seen a higher tested pH the last couple of weeks leading me to believe the organics the soil contained are about spent.

Ms. Walstad moderates a thread at APC.
http://www.aquaticplantcentral.com/forumapc/el-natural/
(IMHO) she's the guru on this style of tanking.


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post #4 of 8 (permalink) Old 10-11-2009, 02:00 PM Thread Starter
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Thanks for the replies,

I've known for a while that my tap water (from a well) comes with lots of CO2; and that explains the rise in pH. What has left me puzzled is how come pH is rising even in an NPT with lots of decomposition going on

I see the soil and plants gassing (pearling) all the time. So whatever CO2 is coming from the soil plus a little bit from food decomposition must be what's sustaining the plants.

The biggest issue i think is the decreasing hardness. This is the first time i have ever dropped hardness in a tank. It seems like the plants are stealing the water's hardness at a high rate, in search for C and minerals ???
EDIT: i have only 1 Vals... i'd be surprised if it alone is eating through carbonates....

Thanks for the pointers...

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Ms. Walstad moderates a thread at APC.
(IMHO) she's the guru on this style of tanking.
I know. I'm a member
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post #5 of 8 (permalink) Old 10-11-2009, 06:54 PM
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yes, it's quite common.
did you add shells or limestone in the substrate?

I cheat all the time and add K, Ca, and Mg in my NPT.


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post #6 of 8 (permalink) Old 10-11-2009, 07:42 PM Thread Starter
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Nope, no limestone/shells....

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Originally Posted by mistergreen View Post
yes, it's quite common.
did you add shells or limestone in the substrate?

I cheat all the time and add K, Ca, and Mg in my NPT.
I didnt add anything to the substrate. I didn't because my water is pretty hard to begin with (i have other tanks and in general they keep and even increase the hardness). For this one, i didnt want to mess with the chemistry; since soil is pretty much unpredictable, i wanted to minimize unknowns.

Also, this tank is more for softer-water fish so i was hoping to have a lower pH than in my other tanks. But not hardness... this caught me off guard.

I have plenty of ways to increase hardness, or i can do with water changes... since the tank is outdoor, a WC is more like watering the outside plants...... but i REALLY was avoiding WC's and dosing! (its a 200 Gal). Guess i'll just monitor and cheat if i have to. I'll start with Excel, hopefully it will kill some algae and perhaps make the plants not steal C from the water.
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post #7 of 8 (permalink) Old 10-11-2009, 09:38 PM
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Quote:
Originally Posted by f1ea View Post
I didnt add anything to the substrate. I didn't because my water is pretty hard to begin with (i have other tanks and in general they keep and even increase the hardness). For this one, i didnt want to mess with the chemistry; since soil is pretty much unpredictable, i wanted to minimize unknowns.
You're suppose to. it has nothing to do with water chemistry. It's to keep your soil from going acidic and also provide Ca and Mg if you add dolomite.

Quote:
Also, this tank is more for softer-water fish so i was hoping to have a lower pH than in my other tanks. But not hardness... this caught me off guard.
soft water fish likes soft water (low GH & TDS).. it has nothing to do with Ph directly.


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post #8 of 8 (permalink) Old 10-12-2009, 03:58 PM Thread Starter
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Quote:
Originally Posted by mistergreen View Post
You're suppose to. it has nothing to do with water chemistry. It's to keep your soil from going acidic and also provide Ca and Mg if you add dolomite.


soft water fish likes soft water (low GH & TDS).. it has nothing to do with Ph directly.
I understood that when your source water was hard (mine is KH 7, GH 13) you didnt need to add 'buffers'...

More or less in general, softwater fish like also lower pH. And ussually, softer water tends to be more acidic. pH is more related to CO2, but in this case i thought the decomposition processes were going to lower pH at least a little bit more than where it is right now...
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