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Re: Nitrate additions

I wrote:

 >> I don't think so. When my tank was N-limited and high in phosphate, I had
 >> every algae imaginable. I've been adding KNO3 over the last month or so,
 >> and the algae has only decreased. I haven't seen any type of algae increase
 >> at any time. (They aren't all gone, but it's much better than it was.)

...and Roger replied:

 >Actually, by definition if nitrogen is growth limiting and you add a
 >usable nitrogen source (e.g. nitrate) then you will get a burst of growth
 >- - usually from the algae. The only time you won't see this is if there is
 >something else in there that is very nearly as limiting as the nitrogen.
 >If you add nitrate and you don't see a sudden increase in growth then in
 >all probability nitrogen wasn't the limiting factor to start with.  If
 >you do get a big increase in growth then you can expect this to continue
 >until some other factor becomes limiting.  That can take a while.

In my case, I *did* get a sudden and dramatic burst of growth. But only 
from the plants. Therefore I assume that while the plants (mostly 
fast-growing varieties) were N-limited, the algae wasn't. Apparently algae 
can do well with large amounts of phosphates and tiny amounts of nitrates, 
or at least some species can. BGA, for instance, has never appeared in my tank.

Most likely, since the fish and their food were adding some nitrogen to the 
tank, the plants were not N-limited all the time. They probably sucked the 
ammonia out of the water in the first few hours the lights were on each 
day, after which the algae *and* the plants became N-limited. But while the 
plants grew perhaps a millimeter or two in those few hours, the algae grew 
much more. (I had one species of soft, hairlike algae that could grow about 
4 inches per hour!)

Alternate theory: the algae used the nitrates so fast and so efficiently 
that the plants were kept in a completely N-limited condition, although the 
algae wasn't short on N at all.

I know none of the trace elements were limiting at the time, I was adding 
entirely too much Flourish. It is possible that potassium was also 
limiting, though. At any rate, adding KNO3 and some extra potassium 
(gluconate) has worked wonders... I've now gone two weeks without sticking 
a hand into the tank to remove algae.

Now I just need to do a major pruning, as hornwort and H. polysperma 
"tropic sunset" have nearly taken up all of the water space in the tank. :)

michael moncur   mgm at starlingtech_com   http://www.starlingtech.com/
"Try to relax and enjoy the crisis."           -- Ashleigh Brilliant