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On Tue, 21 Dec 1999, Dan wrote:
> OK, this is probably a dumb question, but here it goes. With all the current
> postings about overcoming nitrogen deficiencies by dosing with KNO3, or
> supplementing with Jobes sticks, why couldn't a liquid houseplant fertilizer,
> such as Liquid Miracle-Gro, be used as a supplement? According to the back,
> this contains, "Total Nitorgen 8%. 1.2% ammoniacal nitrogen, 1.2% nitrate
> nitrogen, 5.6% urea nitrogen. Available phosphate P2O5 7%. Soluble potash
> K2O 6%. Iron 0.10% chelated iron.
In the simplest analysis, Liquid Miracle-Gro and other houseplant
fertilizers aren't intended for aquariums and shouldn't be used for
aquariums. The risks are reduced for time-released solid fertilizers like
osmocote and Jobe's sticks, but the risk is still there. I use Jobes
sticks because I have found the risk acceptable.
In more detail...
If you aren't going to worry about the phosphate, then try worrying about
the ammonia. Nitrate adds only about 15% of the total nitrogen supply.
The remaining 85% is either from ammonia or from urea which hydrolyzes
in your tank to form ammonia.
If you use this to maintain nitrogen equivalent to the 5 mg/l of nitrate,
then you will be keeping 1.24 mg/l of ammonium. According to data from
EPA, at pH 6.5 that translates to enough ammonia to kill or damage
sensitive fish. At pH 7 that may kill or damage a lot of things.
Also, both assimilative uptake of ammonium and nitrification produce acid
that attacks the buffering capacity. Each mg/l of ammonium that gets
nitrified can consume 5.6 mg/l of alkalinity, or about 0.3 degrees Kh.
You don't have to keep that up very long before your water has no
buffering capacity left. If the ammonium is assimilated instead of
nitrified, then the effect is smaller.
A few years ago David Web reported the results of dosing his low-tech tank
with an ammonia solution. I recall that he dosed a few drops daily for 2
or 3 months and at the end of that time the buffering capacity was pretty
much gone and the pH was dangerously low.
I also recall that others have reported success using urea as a nitrogen
source, and certainly it's possible. To use it safely you would need to
dose moderately, maintain low pH and change water regularly.
All in all, if you're going to add chemical nitrogen then you're probably
much safer adding it as nitrate.