pH KH Dilemma. Chemistry Folks, HELP!

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tomm10

Prodigal Son
Oct 15, 2003
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Oxford, MA
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I posted a while ago that my 29g tank had a high pH and a low GH and KH. The pH is at 8.0 and the GH and KH are both at 40mg/l.

I would really like to get this pH down somewhere closer to 7.0 or even 7.5 but I'm terrified of messing with it since the KH is so low. I haven't even put driftwood in there for the clown pleco because I'm worried the tannins in the wood would drop the pH and the low KH would allow a crash.

RTR suggested that maybe I had too much surface agitiation and that, coupled with a lot of plants, was causing these numbers. I had a Fluval 204 and a Penguin 125 on the tank. The penguin was removed a week and a half ago and as of last night (4 days since last water change) the readings were the same.

Water from the tap tests the same for KH. I didn't check it for pH but my new 10g puffer tank (set up for a week and a half) yields the same test results as the 29g across the board.

There is no driftwood, crushed coral, or other buffering material in the tanks. Both tanks are heavily planted. In fact, even dosing 5ml of Flourish twice a week, the 29g still showed 0 nitrates last night.

I'm a big believer in adding as little as possible to the water to affect the chemistry but I fear the low buffer of this water. I know I could add peat moss or even a piece of driftwood to lower the pH but I am definitely fearful of making to drastic a move and crashing the tank. I've thought about adding crushed coral to the filter but then I'm worried about the pH rising even higher.

Any thought on how to get this buffer up and pH down would be appreciated. I'm not so great at this chemistry stuff.

Readings:

ammonia: 0
nitrites: 0
nitrates: 0
pH: 8.0 (hard to read with teh test kit so that could actually be 8.2!)
GH: 40mg/l
KH: 40mg/l

The readings are the same for both the 10 and 29g tanks.

Tom
 

schiejr

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Mar 18, 2004
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What is the reason for lowering the pH? Are your fish having problems or is it for the plants? Mine runs 8.5 but I also have very hard water so I am not used to no buffering and cannot help with that aspect.
 

happychem

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Dec 9, 2003
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Tom,
I don't think that I remember the original post, but you allude to lots of plants. Do you have CO2 injection running? It doesn't look like it from the numbers, but perhaps this could help.

From your GH/KH readings it looks like all your hardness is carbonate related, or at least, most of it.

The equilibrium between carbonate, bicarbonate and CO2:
CO3-- + CO2 + H2O = 2HCO3-

Is a possible explanation, although, since I didn't read (or don't remember) what RTR said about the surface agitation and plants, you may already know this, if so, I apologize for the repetition.

Basically what this equation sais is that surface agitation will bring your water CO2 concs to atmospheric, which is lower than we want for driving plant growth.

Plants also have a net uptake of CO2, so you're pulling the equation left. Since it appears that you have pretty soft water, as do I, this may be the source of your pH increase.

CO2 and some crushed coral may be the route to go. But I'm not wise enough in the aquarium ways to suggest it. Maybe one of the more experienced aquarists can be a little more critical?
 

tomm10

Prodigal Son
Oct 15, 2003
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Oxford, MA
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schiejr, I'm more concerned about raising the KH that lowering the pH. However, since 8.0 is getting to an extreme end of the pH scale and raising KH generally reuslts in a higher pH I really need to consider the effects on both.

happychem, here's the link to the previous thread: http://www.aquariacentral.com/forums/showthread.php?s=&threadid=27429

I do not have CO2 injection at the moment although I do have a kit I could install. RTR mentioned specifically that this could be a concern though causing a crash.

Tom
 

happychem

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Dec 9, 2003
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Yeah, I see what he's saying. I agree too that adding CO2 to water with next to no buffer is a cause for concern.

As he points out though, at that pH, you're unlikely to see much dissolution of crushed coral, after all, that's the pH that coral grows at naturally.

You've got a tough situation high KH and pH and it's tricky to increase KH without increasing pH. If you're up for the experiment, I think I would try a source of CO2 in conjunction with coral. As the pH starts to fall, the coral dissolution should increase to balance it out. It's an uncomfortable idea though, relying on the response of the coral to balance the pH. But I think that in this situation, this may be the only thing that would solve the problem.

My only advice is that if you do go this route, start the CO2 off slowly and monitor pH and KH carefully.
 

RTR

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Oct 5, 1998
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As I remember, the pH:KH:CO2 came out out less than 1ppm CO2, which is below atmospheric equilibrium. That is probably not accurate without lab meter testing, but it is close enough for tanks. I think that the tank does have significant aeration.

My confusion comes from how the pH gets so high without KH or other obvious alkaline supplement to keep it there. KH of 40ppm just is not generally enough for support of pH 8.0 or above in a functioning biosystem. But I have never worked with such low-buffered water and am in the dark.

If I had such water to work with myself, I'd hit the water company for test results and the full process technique on the water to try to get some understanding. If I had to wing it, I'd add some sodium bicarbonate to a KH ~60-70ppm in a bucket or spare tank and add CO2 and monitor pH/KH/CO2 for some days. If that gave reasonable results - some degree of stability and reduced pH with higher CO2 (15-25ppm), I'd use aragonite in a filter to bring the tank KH up, damp the surface breaks way down and run CO2. I don't think I'm brave enough to add CO2 without a KH of at least 4 degrees (~70ppm).

Such a planted tank without some mods is always going to be carbon-limited and potentially unstable IMHO. If biogenic decalcification starts up (Vals especially) the pH will skyrocket - that process generates hydroxide ion (OH-) and precipitates calcium. It is not really very common in tanks, but a potential mess.
 

tomm10

Prodigal Son
Oct 15, 2003
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Oxford, MA
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Alright, so if the crushed coral is not going to do much to raise the KH, would it also be safe to assume its not likely to raise my pH much either?

My thought is that I could add crushed coral in small amounts over time. If the pH begins to climb, as long as the KH increases I could begin a monitored CO2 injection to lower the pH.

This is really beginning to feel like a high wire act.

Tom
 

tomm10

Prodigal Son
Oct 15, 2003
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Oxford, MA
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Originally posted by RTR
As I remember, the pH:KH:CO2 came out out less than 1ppm CO2, which is below atmospheric equilibrium. That is probably not accurate without lab meter testing, but it is close enough for tanks. I think that the tank does have significant aeration.

My confusion comes from how the pH gets so high without KH or other obvious alkaline supplement to keep it there. KH of 40ppm just is not generally enough for support of pH 8.0 or above in a functioning biosystem. But I have never worked with such low-buffered water and am in the dark.

If I had such water to work with myself, I'd hit the water company for test results and the full process technique on the water to try to get some understanding. If I had to wing it, I'd add some sodium bicarbonate to a KH ~60-70ppm in a bucket or spare tank and add CO2 and monitor pH/KH/CO2 for some days. If that gave reasonable results - some degree of stability and reduced pH with higher CO2 (15-25ppm), I'd use aragonite in a filter to bring the tank KH up, damp the surface breaks way down and run CO2. I don't think I'm brave enough to add CO2 without a KH of at least 4 degrees (~70ppm).

Such a planted tank without some mods is always going to be carbon-limited and potentially unstable IMHO. If biogenic decalcification starts up (Vals especially) the pH will skyrocket - that process generates hydroxide ion (OH-) and precipitates calcium. It is not really very common in tanks, but a potential mess.
Oy.

Okay, I'll hit up the water company for info and go from there. Never occured to me to set up a trial tank to test the water. there goes my theory about my being a genius. Thanks guys.

Tom
 
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