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If you now acknowledge that there are statistically significant differences between the two meters, why did you write, "measurements were surprisingly close" in your closing and leave it at that? Hobbyists should be given all the facts and analyses. You may consider the differences minor, but...

Dana, I had one additional question. You observed that the sun setting was closer to the LiCor than the electric setting, but you didn't address the question of why in the article. This multiplier is just an arithmetic term in calculating PAR, so the sun setting simply increases the calculated...

Dana, I agree with you completely. You've made the case for using a spherical sensor in a reef tank, which is why we questioned the use of a flat sensor in Mike Kirda's article. With the ability to integrate light coming from all directions, it can more accurately tell us what light is reaching...

Dana, it is ironic that the editor of Advanced Aquarist would challenge posters to avoid ad hominem comments and you as the author of the article in question would then post a reply filled with them. The value of a study is only as good as the methodology used to gather the data. If there are...

Dana, I would encourage readers to look at the Apogee review I wrote for Advanced Aquarist many years ago. It can be found at www.reefkeepers.info under the lighting section. It will provide additional information not found in your article. I hope you'll take time to clarify some points of...

Eric: Orthophosphate around natural reefs generally measures about 0.01 ppm and the instructions that come with Rowa Phos state, "the phosphate concentration should always be kept below 0.015ppm." You may consider 0.03 ppm low, but ideally levels should be half that. It is true that it is...

Randy, nice article. The following may strengthen your skepticism. My tank measured .24 and a friend's tank measured .23, and the kicker is that a pristine reef in the Pacific measured .20. There seems to be a pattern. :) Richard

Silicon measured 0.41 mg/l compared to Ron's IO of 1.50

Hi Randy. It replicated Ron's work. It was ICP.

Hi Greg. You are correct. All the numbers are in mg/l. Cobalt and lithium were considerably higher than Ron's numbers for IO, as was chromium. IO had detectable tin, antimony, nickel, zinc, and others while Marinemix did not. That's why I said it is a different mix of metals. The numbers are...

The metals were measured using the same methods Ron used, so the numbers are comparable. The tests are part of a larger project that I'm working on and all the details will be presented when I write everything up. The results suggest perhaps that some of the problems experienced switching over...

Here's something to ponder while we await the testing of other salts. Here's what Marinemix Bioassay looks like in mg/l: Aluminum .23 Boron 7.8 Barium .034 Cobalt 24. Chromium .046 Copper .009 Lithium...

Mike, the "might" refer to the size of the error, not the fact that potentially significant errors are introduced by the sensor's insensitivity to shorter wavelengths. There's no question that higher Kelvin bulbs are going to read low, it is just that each brand of bulb is going to have a...

Charles, some rough calculations suggest that there are other more serious errors associated with the Apogee sensor. Traceable sensors like LiCor's are nearly flat with a slight roll-off in sensitivity close to 400 nM. The Apogee is far from flat. Sensitivity is only 30% at 400 nM and nearly...

When I am measuring, for example, levels at the cap of a leather coral, what benefits exactly does a 4pi sensor give me? None. Unless the leather coral itself is emitting light. Actually Mike, the leather doesn't have to emit light, it just needs to reflect it. Every non-black surface on a reef...

Unfortunately true. In my experience, none of the Zebrasoma school. They tend to keep an eye on each other when they think there might be food involved, but otherwise they go their own way. Even with a tank 23 feet long, there isn't much schooling activity with any of the fish. Acanthurus tend...

Mike: Charles brings up a number of issues that unfortunately compromise the value of your measurements and observations. There are a number of reasons the LiCor sensor costs over five times as much as the Apogee sensor. You dismiss these differences as inconsequential, but they are not. The...

I didn't write that the Blueline is brighter. I wrote that the AB bulb is not brighter. There is a difference in the two statements. 72 vs 77 is within measurement margin of error and bulb variability for these kinds of measurements. What it means is that we can't say that either bulb is...

I'm glad you found the article useful. I'll be doing some additional work and I believe Sanjay is working on an article. The challenge is determining what to test. There are four or five luminaire geometries, a couple of bulbs in each wattage, and several ballasts to consider. That adds up to a...