Whoops! Right you are, I have my "N's" reversed. That was embarrassing. I
agree that Nitrate is unlikely to be the problem. The stats were provided in
order to rule it out but, instead, I just made it even less clear.
Apologies.

I'm dosing with Fe because it's all being used, and I'm trying to give my
plants a leg up on the algae. Is that wrong?

I've actually stepped back my lighting from 220 watts but am adding CO2
because it helps lower my Ph and, according to the "Determination of CO2
Content in Aquarium Water" table I'm using, with ph of 7.5 and Kh of oh,
say, 15, I expect the CO2 content to be about 11 mg per quart which would be
at the low end of desirable, or do I have that muddled?

I'm still getting around the idea of carbonate hardness which I had rather
thought in my muddled way to have been subject to "manipulation" as opposed
to Gh aka permanent hardness which is, well, permanent. At any rate, I'm
using coarse gravel out of a bag from Petco, brand and chemical composition
long since forgotten, but the standard stuff.

At any rate, thank you very much for your help. It was not the answer I
expected and, in my experience, those are almost invariably the ones which
are correct.

One last question. Would you even attempt to maintain a Ph at around 7 if
it comes out the spigot at around 8?

Thanks,
kush

"You can't have everything - where would you put it?"

Dave Millman wrote in message
...
kush wrote:

It's been quite a few years since that chemistry class I never took, so
if
someone could give me a hand here, I'd be grateful.

I've got a 75-gallon standard tank with 110 watts of lighting.

This is low for a plant tank, but acceptable as long as you don't inject
CO2.

The tank has
lots of wood in it and is moderately to heavily planted and I'm
injecting
CO2 through a powerhead and also with a diffuser next to the filter
output.

Oops! High CO2 plus low light. This is an imbalance which often causes
algae
soup.


I have a pretty heavy fish load for a planted tank, but my maintenance
is
impeccable (imho).

Ph.............7.4-7.5
Nitrate.......not measurable
Nitrite........ 0.5 ppm
Gh.............3º
Kh............. 12º
Fe............. not measurable

I say the carbonate hardness is not measurable because after 12 drops it
just turns the same colour as the test liquid.

A bit of confusion perhaps...

Nitrate with an A is the end result of the nitrification cycle. It is
extremely
unlikely that it is unmeasurable in a heavy fish load tank, although
measurements under 5ppm are common when the tank is also heavily planted.

Nitrite with an I is an intermediate product of the nitrification cycle.
In a
mature tank, it goes to zero and stays there forever. It is also toxic to
fish.
Is it possible you have reversed these measurements?

In any case, Plants cannot grow without Nitrate with an A, as it is an
important
macronutrient. Given that you are dosing micronutrients such as Fe, you
are
probably creating a substantial imbalance.

Regarding your KH and pH, these are probably not your problem, although it
would
be interesting to know where all that KH is coming from. What kind of
substrate
and stone is in the tank?

Recommendations: Your light level is too low for a CO2 tank. Either stop
injecting CO2 or double your lighting.

Untangle your test results to figure out actual levels of Nitrate with an
A and
Nitrite with an I. If Nitrate is actually unmeasureable, you will have to
dose
KNO3 to allow plant growth.

These links are all from the group FAQ:

Background on water hardness:
http://faq.thekrib.com/begin-chem.html

Lighting:
http://www.thekrib.com/Lights/
http://faq.thekrib.com/plant-lighting.html

Nitrate and test kits:
http://faq.thekrib.com/begin-tests.html