Aquarium Math. - The Planted Tank Forum
Old 10-26-2006, 04:22 AM Thread Starter
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Join Date: Oct 2006
Location: Florida
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Aquarium Math.

Although you can go to several pH, KH, and CO2 relationship charts...most of which also indicate the formula for CO2, I thought I'd list a couple of others that I figured out so that any one looking to adjust their PH by altering their KH can easily input the numbers. I've punched the formulas into MS Excel and it's much easier to do than messing around with a calculator.

Everyone can find CO2 = 3 * KH * (10^(7-pH))

But, if you wanted to adjust your pH by altering your KH, you could look at the chart or punch the numbers in this way: KH = (CO2/3)/(10^(7-pH))

Just for kicks, if you wanted to find out a hypothetical pH, given CO2, and KH: pH = (LOG(CO2/3/KH)/LOG(7))-7

You can easily make a calculator in MS Excel given the above formulas to calculate this.

Also, if any DIY'er is interested, and uses MS Excel, I have a spreadsheet that calculates tank volume, weight, gallons, and glass thickness with an adjustable safety factor. Just send an e-mail asking for it.

If this is old news....sorry! I didn't see it in a search.

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Lycosa is offline

Old 10-26-2006, 04:27 AM
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Join Date: Mar 2006
Location: Indianapolis, IN
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For only having 12 posts, you sure have said some useful stuff!!

Welcome to PT.net!

That spreadsheet would be awesome to play around with - mind sending it to me? jen dot ford at gmail dot com. Thanks!

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Old 10-26-2006, 04:49 AM Thread Starter
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JenThePlantGeek, I sent it to you. Although I protected the sheet to keep the formulas from being erased, to use the spreadsheet, just enter the values in the 'light yellow' cells. Just enter the 3 values for length, width, and height. The rest of the values...glass thickness, deflection, volume, etc. are calculated automatically by those values. You can change the safety factor, but 3.8 is considered a safe value. The higher the safety factor, the thicker the glass and less deflection.

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Lycosa is offline

Old 10-26-2006, 04:21 PM
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that is a fine chart, and thanks, but my question is, why would you alter your KH for your pH. pH IMO really doesn't matter that much but metting around with KH is a trickier situation. I may be wrong, but I think this is good for mere understanding of the relationship, but not a useful angle to use when balancing your tank requirements.
fresh_lynny is offline
Old 10-27-2006, 05:30 AM Thread Starter
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Why would I adjust my KH to alter my pH? I realize that there is much debate whether or not it is really necessary. I think that if you have educated yourself enough, then altering the KH is not necessary. If you are just starting out, or do not have the time to devote to your tank, I believe that buffering the water can be a good thing. Some people prefer a large bioload with few plants. In that situation, I would certainly want adequate alkalinity to stabilize pH. I think that there are many variables to consider. For heavily planted tanks with a small biological load, then most nutrients will be assimilated and the KH shouldn’t be a concern.

When people talk about ‘my pH crashed’, I think this is more often than not due to ammonia or CO2 poisoning. I personally have never seen a running freshwater system swing so rapidly that the fish died. (I have seen a reef tank precipitate carbonates…a snowstorm…and then the pH really did ‘crash’ causing a massive die-off). In the case of all aquaria, pH is the effect, not the cause. Is it life threatening to your charges….yes, if done rapidly. Have you ever seen it happen? Probably not, unless you dumped your fish into water with a largely differing pH. I would suspect more that it’s the fish that went missing 2 days ago, a massive die off of nitrifying bacteria, accidentally overfeeding, and the resultant ammonia spike that killed the fish. Having freshwater systems, we are lucky because the fish are much more adaptable than their marine counterparts. To avoid a dissertation on the variables, we could generally agree that freshwater bodies are subject to much higher deviations from the targeted water parameters we have been taught to keep our tanks at. However, this advice was/is good considering that a percentage of us will never devote enough time to the hobby to become ‘advanced aquarists’.

It is my belief that unless you are willing to devote the time to learn about the chemistry behind the numbers, then shooting for an adequate alkalinity as a safety net against the effect of CO2 or metabolized acids can be a good thing. I’m not saying that alkalinity will keep the fish alive even though a pH controller failed and the CO2 has reached toxic levels, I’m saying for a newbie, keeping pH at a consistent level when all other variables are unknown, or not understood is a benefit to the fish and the system itself.

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Lycosa is offline

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