OK - water this time.
First off, testing. I am looking at some kits and I like the Hagen Master kit, for its breadth of tests. Can be gotten (relatively) cheaply at thatpetplace for $65 total. I wrote Hagen to ask them some questions, one answer was that each test has enough reagent for 50-100 samples. I asked about the sensitivity of the tests and I stumped the respondent.
What are the thoughts on this test package? With my background, I am totally at home in matching color charts, it is a non-issue for me. Are the tests fairly reliable and the gradations from color to color not too large?
Second - tap. I have a well, should be fairly hard but I have no numbers. I don't expect any issues here, may even have the benefit of a little extra Ca
Third - flow. I bought a Rena XP2. Will this give me enough flow and turnover (55g)? I've read turnover rates of 5x, 10x, etc. What is the time basis in these numbers, hours? Is this sufficient (see #4 below) for oxygenation? The LFS
had no air pumps at all on any of their SW
Fourth - Tank covers. How much is needed to be exposed to atmosphere? I have a 'classic' 55g tank, 48"x13" (roughly), is this surface area/volume ratio high enough I can have some covering or do I need it totally open? The lamp fixture (260W) will sit about 5 inches above the tank top.
OK - now time to contribute something, probably only for the DIY'ers but here it goes anyways:
pH - pH is measured using a glass pH electrode. This electrode generates an internal potential depending on the number (or lack) of hydrogen ions on the outside surface. This potential is compared against a reference electrode. A reference electrode is typically a simple electrode consisiting of a solution of KCl saturated w/ Ag (silver). The solution is kept in place with a porous plug of some sort. The solution must be allowed to slowly weep though this plug into the solution where the pH is being measured.
Many pH electrodes are what are called 'combination' electrodes. That means that the reference and measuring (pH) electrode are combined into one. If you have one of these take a close look at it and you should find a tiny orifice somewhere near the bottom. This is the porous plug to the reference electrode. It may be white as ceramics are a common material for these plugs.
The measuring of the pH can be done simply with a voltmeter. Place the positive lead on the pH electrode wire and the negative on the reference wire. If it is a combination electrode there may only be one wire, with a BNC connector on the end. In this case place the positive lead on the center conductor and the negative lead on the outside of the connector (connected to the shield in the cable which is what the reference is tied to).
A glass pH electrode gives a voltage of 60 mV for every pH unit. A pH of 7 is 0 mV, this is your starting point. Acidic pH's are + mV and alkaline pH's are - mV's. Knowing all this, a tank with a pH of 8.2 should give a mV reading of -72 mV.
Now the rub. The reference electrode over time becomes contaminated, it is a porous plug after all. This causes the mV reading to drift to zero, even for the same pH. In the above 8.2 pH sample, you may get a reading of only -30 mV after even a couple of months of use. This is totally natural and the proper behavior of the electrodes. That is why you have to calibrate with buffers from time to time.
In the voltmeter reading scenario, to get an accurate pH reading you would have to take some measurements and plot the points. To do this you need two (three is better) buffers. In a SW
aquarium, buffers of 7 and 9 would be perfect.
Measure the mV reading with the electrodes in each buffer and plot them. Be sure to mark the x- and y-axis with the proper units and values. Connect the two dots (if three you may have to 'fit' a little) and you now have a calibration curve.
Using this curve you can now take a raw mV reading from the electrodes and get the appropriate pH.