Trying to understand KH - PH - Co2 - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 11-19-2006, 06:45 PM Thread Starter
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Trying to understand KH - PH - Co2

My KH is 3 dh and my PH is 6.8 so according to the charts my Co2 levels are at 14 ppm which is enough for my lightly planted, 1.5 wpg, 70 g tank.

BUT, I have been having problems with high phosphates (which appparently negates the chart readings). So I've got my phosphates down to 0.5 using PhosGuard in the cannister filter. My KH and PH still read the same. There are no buffers added.

So am I correct in assuming I have ample Co2? Where is it coming from? Respiration from the fish (3 - 3" goldies)? I only do a 15% water change and am not dosing ferts yet, which brings me to my 2nd question:

The tank is cycled (AM. - 0, Nitrites - 0) but I consistantly get readings of maybe only 1-3 ppm Nitrates. Why isn't there more? I thought goldfish were such heavy waste producers that my Nitrates would be a constant problem requiring big water changes? I also thought I read somewhere that there was a correlation between high phosphate and low nitrates. Is there?

I didn't want to start dosing until I solved the phosphate problem which was causing cloudy water (and possibly a bacterial bloom at the same time) and now that the water is clear I thought the nitrates would go up, but they didn't so I'm a bit confused.

Any thoughts on this would be appreciated.

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post #2 of 8 (permalink) Old 11-19-2006, 07:01 PM
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Phosphate has nothing to do with the KH chart...
If you are not adding any C02 to the tank, then you do not have any in the tank, therefore rendering the chart useless anyway..

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post #3 of 8 (permalink) Old 11-19-2006, 07:07 PM Thread Starter
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I've been looking at Chucks planted aquarium page for the C02 - KH- PH charts and he says :

"NOTE: This calculator (and the chart based on this formula) will only work if your water is carbonate buffered. If your water contains high levels of phosphates, it will alter your water properties, and invalidate these CO2 calculations."

Here's the link:

Measuring CO2 levels in a Planted Tank

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post #4 of 8 (permalink) Old 11-19-2006, 08:07 PM
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There is another note just above that one:
NOTE: If you aren't adding CO2 to your water, and the CO2 level based on the pH and KH indicates more than 5ppm, then it is very likely that some other buffer (such as phosphate) is present in your water. In an inhabited aquarium, the amount of CO2 produced by the fish will not have an effect on CO2 levels in the water. Any excess CO2 created by fish will dissipate into the air, leaving a fairly constant CO2 level of about 3-4ppm. If you test your pH and KH, and without adding any CO2, the chart says you've got 20ppm CO2, don't believe it.

My whole point being that if you are not injecting C02 then the chart will do you no good in the first place, with 1.5wpg and a very light plant load, you won't really need any C02.
I also wouldn't dose any ferts either with a tank like that, you will need more plants, maybe some ferns and moss, then and only then would I dose, and at that just a little K+ and a touch of Trace.. use the fish food, waste for the rest.
Now if you increase the lighting you are getting into another deminsion, whole new story with the changes that will happen.

Hard to say what your nitrate level is and how you tested and with what kit you used and how you used it and also how you interprit it, you may or may not have more N03 in the tank than you think, goldies are waste producers.
Why not just do more frequent water change to control the P.

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post #5 of 8 (permalink) Old 11-19-2006, 08:14 PM
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Two points:
If you don't add CO2 to the tank the water will be in equilibrium with the atmosphere which will give you from .5 to 3 ppm (roughly) of CO2 in the water.

It isn't hard to accurately measure KH with a test kit, but accurately measuring pH isn't easy with a similar quality test kit. That involves judging very small differences in color. So, my guess is that your 6.8 pH reading is off, and the real pH is more like 7.6 - the conventional yellow to blue pH test kit doesn't work at all in that range, and the "high range" pH kit, yellow to red, as I recall, still requires a judgment of degrees of orangeness to read accurately.

At 1.5 watts per gallon CO2 is desirable, but not necessary anyway, and if it is 20 gallon or less, Excel is an economical way to supply the carbon the plants need. (Or do a Natural style tank, with no added ferts.) Don't try to measure nitrate, phosphate, iron, etc. and rely on those measurements unless you get good test kits and carefully calibrate them.

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post #6 of 8 (permalink) Old 11-19-2006, 08:56 PM Thread Starter
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Quote:
Originally Posted by WfxXx View Post
Hard to say what your nitrate level is and how you tested and with what kit you used and how you used it and also how you interprit it, you may or may not have more N03 in the tank than you think, goldies are waste producers.
Why not just do more frequent water change to control the P.
- I'm using the AP test with drops - there is essentially no color change, it stays yellow (maybe slightly darker yellow, which is why I estimate 1-3 instead of 0) I'm very careful to shake the bottles and wait the correct amount of minutes as per instructions. I tested the kit with a different water source that has known nitrates and it did work on that source.
So, again, where are my nitrates? Is it possible that my plants are consuming all of them?

- I tried large, frequent water changes for the phosphates, which reduced the cloudiness a little, but it would come back in a day (phosphates in my source water are 0.5) This is why I'm not sure if I was having a bacterial bloom at the same time. Any way it seems to be stable now.

- Ok I understand more about the co2, now. I think. Once I start injecting it (if I ever do) my parameters will change a bit, and the chart will become more useful?
But, if like Hoppy says, the test kits are basically useless, then its all just guesswork for those of us who don't want to invest in more expensive kits. Oh well.

Thanks for all the help, I know this isn't really a "planted tank" But I love the way it looks. The anubias and the moss balls are doing great as things are, the vals - well, hanging in there is about it. Planted in Eco-complete in glass vases. The one in the right hand corner behind the driftwood is the best - well rooted and no dying tips.

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post #7 of 8 (permalink) Old 11-19-2006, 09:15 PM
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after seeing the tank i think your readings are accurate.your fish load isn't really that high.if the tank is old enough it should be taking care of most of your nitrates by itself.maybe try very little potassium and some diy co2 and see if the tank takes care of the phosphate levels for you.you have low light and a low plant load so i would dose sparingly and see what happens.
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post #8 of 8 (permalink) Old 11-20-2006, 01:13 AM
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Quote:
Originally Posted by dymndgyrl View Post
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So, again, where are my nitrates? Is it possible that my plants are consuming all of them?

- Ok I understand more about the co2, now. I think. Once I start injecting it (if I ever do) my parameters will change a bit, and the chart will become more useful?
But, if like Hoppy says, the test kits are basically useless, then its all just guesswork for those of us who don't want to invest in more expensive kits. Oh well.
I'm not saying the test kits are worthless. But, the normal pH test kits we use will measure pH between about 6.0 to 7.2, and it is easiest, by far, to differentiate between the colors when the kits are used at a pH of 6.4 to 6.8. Then you are seeing yellow green become green become blue green. But, at the ends of the scale the color changes are very small and hard to read. If you were injecting CO2, and using enough of it, you would have a pH of about 6.5 or so, right where the pH kit is most usable. You can easily get around the problems with measuring CO2 with KH and pH by using a "drop checker".

Nitrates are used pretty rapidly by growing plants, so if you are not dosing nitrates, but relying upon the tap water and the fish for it, I would expect that you would have a pretty low level in the tank most of the time. As long as you don't have high light intensity that shouldn't be much of a problem.

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