Question on testing of pH:
I have been mixing my own potting mix for the last six months now, and testing it for Ph after adding Dolomite. My' tester' is a little bottle of solution, and powder that you sprinkle on it, and then compare it with the chart. I always feel that it is not that accurate as you can get different readings.My question is, is there a better way to test? I thought there might be a probe (electrical) on the market, but I have'nt found anything when I Google it on the internet.

Answer: 
The kind of test kit you have is usually quite reliable. Almost all the African violet growers I know of use them. There are a few things, though, that you must keep in mind.  

 Firstly it is best to leave the mix for at least two weeks for the dolomite to act on the peat and other ingredients before testing. If you test too soon, you will find that you are recording the pH of the individual grains of the different materials in the mix sample you took. Let the mix mature longer and the pH will become more uniform.

 Secondly, some of the charts sold with the testing kits of the kind you have can be unreliable. Those that just show colours printed on a piece of light cardboard can vary quite a bit with different batches of kits. They are at the mercy of the printing process. More reliable are those sold with a chart that has a series of colour chips glued onto the cardboard. I have three printed kits in my possession and the colours are different from each other. Only one is similar to that of the colour chips on another. If you have one of these charts, what you would need to do is somehow to establish whether your printed chart is showing a correct colour (perhaps by checking against a chart made of colour chips).

 One can buy fairly cheap probe type pH testers, but my understanding is that they are often unreliable.

 I finally solved my dilemma by purchasing a laboratory tester. This is an electronic instrument that is very accurate if used according to instructions. It needs to be recalibrated regularly (using special, available calibration solutions). Distilled water is used with a sample of potting mix. Best results occur if the potting mix grains are broken up a bit before testing. The probe is stood in the mixture and left for a few minutes for the pH reading to stabilise.

 The disadvantages of this are: cost (over $150 when I purchased a couple of years ago), need for regular purchase of distilled water (not all that expensive), and need to purchase new calibration material on a regular basis.

 Mine is a Eutech Oakton Waterproof pHTestr 10 (see this website: http://www.eutechinst.com/pdt-para-ph-phtestr10.html), and I purchased it from Envirosensors at Cremorne, Sydney. There are likely to be other places one can purchase such instruments if you want to be really sure of the results of your pH tests.

Chapters 6 of "African Violets for Everyone" has a full treatment of the subject of pH.