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Nitrate, CO2, Fe



About 2 month after I set up my planted 29G tank,
the whole thing looked great and there was essentially
_no_ algae at all in the tank. The plants are
growing like crazy and cutting them once a week
is not enough.
So I was getting a little curious because I've read
so much about the influence of Nitrates to the growth
of Algae. My Nitrate levels were around 5-10 ppm before
I started the test. Then I raised them (fertilizer
tablets) to about 50ppm (!) and kept this level for
4 weeks. And guess what: nothing changed in the tank.
No Algae were growing, the plants totally behaved like
before.
Also, I raised the Fe level to .5ppm for about 3 weeks
with no visible change in plant or algae growth. What
actually is supposed to happen with a too high Fe level?
.5 ppm did not do anything to my tank. But anyway, when I
stopped fertilizing with Fe (levels dropped to not detectable),
the plants stopped growing and a few were even looking 
very sad, so I started adding Fe again.
A next little test was turning off the CO2 - with an aweful
result. I had to stop this test after 4 days (that was when
I bought the CO2 bottle + regulator - wrote about this
to the list). Several stem plants lost their leaves (so bad
that the whole water surface was covered with dead leaves
after 3 days or so)  and
the leaves of sword plants started decaying or just disappearing
(still have one leave in the tank which looks like a
skelleton). After turning on the CO2 again, about 2 days later
the plants began taking off again and all of them recovered
very good now (2 weeks after the test). Fortunately, I
did not lose any plants, but I'll never do a CO2 shutoff
test again!
Now the tank looks like before the tests (just great) and my question
is: Why did nothing change when I raised the Nitrate and Iron levels
and what is supposed to happen in case if high Fe????
Thank you very much!
by the way: I enjoy this mailing list a lot and keep checking
my mail many times a day to see if there is something new.
Thanks to everybody participating!

Karsten.