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post #3 of (permalink) Old 10-20-2020, 02:27 AM
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My 29-gal is heavily stocked and I haven't used biomedia in many years. BB already exist on every surface in your tank (including substrate) and tubing. Plants will get more access to ammonium (which they prefer) without biomedia in a filter and BB will expand, as needed, to deal with any NH4 that remains. Although I've never measured a TAN spike, if your pH is below 7 there will be none of the dangerous NH3 present, it will all be NH4. So it wouldn't matter if you did get a TAN spike.

Qualifier: I may be resuming use of biomedia. I've been reading some aquaponics and hydroponics articles that claim that NO3 is taken up better, beginning at pH below about 6.2, than ammonium and that the excess ammonium that is not taken up may interfere with the uptake of calcium, magnesium and potassium. Additionally, too much NH4 vs NO3 may actually cause N limitation at these low pH levels. So far in my reading, it seems mainly applicable to the root zone. Apparently, a ratio balance in favor of NO3:NH4 becomes important as acidity increases. I haven't gathered enough yet to make a decision. Perhaps other members may have knowledge of this possibility.
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