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Originally Posted by Myka
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Nice find! I'll read it more thoroughly later. A quick skim, this caught my eye:
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Note that this process consumes alkalinity (the H+ being produced shows this). So when nitrate is accumulating in a reef tank, alkalinity is being depleted. Production of 10 ppm of nitrate will deplete about 0.16 meq/L (0.45 dKH) of alkalinity. If this nitrate is removed by water change, that alkalinity is lost forever. If the nitrate is taken up by an organism (algae, coral, bacteria, etc.) and used, then all of that alkalinity is returned to the system (see equations below showing this fact).
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Curious, when I dose nitrate and the bacteria consume it does that contribute Alkalinity to the system? I know it would be insignificant. If I was dosing an additional 1ppm a day that would equate to .045dKH per day.
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In most cases where nitrate levels have been examined in relation to the growth of calcareous corals, the effects have been reasonably small, but significant. Elevated nitrate has been shown to reduce the growth of Porites compressa (at less than 0.3-0.6 ppm nitrate),16,17 but the effect is eliminated if the alkalinity is elevated as well (to 4.5 meq/L). One explanation is that the elevated nitrate drives the growth of the zooxanthellae to such an extent that it actually competes with the host for inorganic carbon (which is used both in photosynthesis and in skeletal deposition). When the alkalinity is elevated, this competition no longer deprives the host of needed carbon.17
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This makes sense. The higher the nutrients the higher Alk is needed. Likewise, low nutrients generally requires low Alk. Are they suggesting coral growth and zooxanthellae overproduction (browning) happens at levels of .3 to .6ppm? Anecdotal reports 1 to 2ppm being fine... Also, 4.5meq/L is just over 12.5dKH!
Anyway, I'll spend more time with it and wrap my head around it later.
Thanks!