Kh

[simonbrown403]

Reading this on a site i came across, and was wondering if high levels of phosphate would affect, or even carse a high KH readings.

http/aquaticconcepts.thekrib.com/Co2/co2_faq.htm#T07
How accurate is the KH/pH/CO2 table method?
The table is very accurate but your measurements may not be! There are two concerns.

First, you need to think about the resolution and accuracy of the test kits. If the KH kit is accurate to +/- 0.5 dKH and the pH kit is +/- 0.2 units, the range of CO2 values read from the table can be quite large. Let's say you get a carbonate hardness reading of 3 dKH (+/- 0.5) and get a pH reading of 7.0 (+/- 0.2). This would indicate CO2 ranging from a low value to an optimum value:


KH = 2.5, pH = 7.2 >> CO2 = 5 mg/l
KH = 3.0 pH = 7.0 >> CO2 = 9 mg/l
KH = 3.5 pH = 6.8 >> CO2 = 16 mg/l

Also, most KH test kits actually measure total alkalinity. If KH is the predominate component of alkalinity, all is well. However, if other buffers are in the water (phosphate buffering products, for example), you will get a higher "KH" reading and you will think you have more CO2 than you really have.

 

[zig]

Yes this is correct but the levels have to be very high for it to be a concern, it also only really impacts if you also have a very high Ph, it can throw off your co2 measurements, there is a mathemathical formula to correct this but dont ask me what it is, but the phosphate readings would have to be really high say 10ppm plus for it to really make any significient difference.

As the text below states you have more chance of error from testkits not being accurate, and IMO a much wider margin of error even if your your phosphate readings were as high as 10ppm.

There is a formula somewhere that i can dig out if you really want it but like i say your readings would have to be sky high (what we would consider sky high) for it to make any difference.

Other things that would throw off the Ph-Kh-CO2 relationship that are much more likely (other than dodgy testkits) are the presence of phosphate buffers things like Ph Up Ph Down etc. i think even some Discus buffers are phosphate based and if these are present in the water as you take KH readings, you have a good chance some of them will be false.

So basically i wouldnt really worry about it but it can be a factor.

 

[simonbrown403]

Thanks zig.

Another question, i remember reading some where, that's the reading you KH test kits give you are not necessary the true KH.

I belive there is a way of working it out is there a calculator on a site or a formula or something to help.

Thanks

 

[zig]

Im not sure Simon i havent come across or read anything about this, my understanding is that as long as other buffers are not present other than carbonate (from co2) that the Ph KH relationship is fixed for measuring co2.........probably doesnt help much but i havent come across anything else that i can think of right now.

 

[simonbrown403]

Thanks anyway