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Playing with nutrients and test kits

Buying test kits:
You do not have spend a ton of dough on test kits. NO3 is the the only one I
suggest really getting a nice Lamott kit for. pH, PO4 etc etc can be done
with inexpensive kits(SeaChem etc). If you WANT (not need) you can get the
Lamott/Hach kits. If your twisted and interested in things beyond growing
nice plants or want the accuracy and convenience they are nice. pH monitors
are nice but not required.

Testing the nutrients themselves:
In order to gauge a nutrient and it's effect on plant growth (I consider
eukaryotic algae plants) you should define a set of of good parameters for
your test subject, in this case what most folks call higher plants.

I define them as 
CO2: 20-30ppm
NO3: 5-10ppm
K: 20-40ppm  
PO4: .4ppm(hazy on the lower range)-1.0ppm
Traces: Hazy, I go to 1.0ppm Fe or so 1 hour after addition. Some go with
.1ppm. Harder waters will need more.
GH: 3-25
KH: 3 and up
NH4: 0.05 or less
Good tank mixing, filtration etc
Lighting 2-4 watts a gallon

In order to see the relative effects of a single perturbation, you MUST keep
the other nutrients with your set of ranges. Otherwise the resultant will be
a multiple effect. After completing a run of the single variable proceed to
2 variables and then to three etc.

So if you take each nutrient and go from 0 to 10ppm (or whatever appropriate
range you want to use here) and note the effects one at a time you will get
a reasonably good idea of the relative effects of each nutrient.

 Folks with low CO2 will get algae (in this case our indicator
preturbation->poor or low CO2 with high light, PO4, NO3 etc all at the
preset range except for CO2) and poor plant growth. You need to make sure
the other nutrients are in good shape during this period. You will find CO2,
NO3 and NH4 to have large effects. Traces and K will have moderate effects
and oddly, PO4 will have the least effect(K as well but it's not as good in
the low range like PO4).

Since there are other unknowns such as extra cellular leakage and other
organics that we do not or cannot test for, simply doing a large water
change on a regular basis removes most of this build up. One could argue
that more frequent water changes and larger ones are needed but few people
are realistically going to do this. 50% weekly is pretty good size removal
of most unknowns that might build up.

Light and CO2 are another area. I have found even tanks with 1 watt a gallon
benefit greatly from CO2 additions. they can also handle the same levels of
nutrients. One would not expect this but looking closer you find that uptake
rates are proportionately slower. At 1 watt a gallon of light I only does
weekly before getting near zero ppm. At 4 watts a gallon it would take 3
days. Plant and algae growth is slower and the herbivores appear to be more
effective as a result of slower growth.

I came to my levels of PO4 and traces this way. You can as well.
Tom Barr