This can be very tricky when dealing with many variables.
Often the suggestion is "buy a test kit" and test to see
what your nutrient levels are. This works well for CO2
(but folks should double-check to be sure before proceeding) and
GH but the other nutrients like NO3, K, PO4,
Fe as a proxy for the traces are more problematic. Chuck Gadd's
dosing calculator works well for the chemistry challenged.
#2 - Testing
This is huge issue for most folks. Test kits cost as
much as a filter, or much more in some cases. Some folks can afford
nice Lamott/Hach kits, most cannot nor wish to invest $300 in this.
Cheaper kits are not offered for K. NO3 kits are very
problematic and color reading scales are difficult to assess with
cheaper kits. Some folks are color blind. Many folks don't ever
want to test or feel there's no need to test. I fell into that group
for many years. I did as well as I do today but I am much more consistent
now and I also know why it works! Iron (Fe) tests have been a very
contentious issue for me for about 3 years now. I believe I have
a relatively simple methodology to sidestep much of the drudgery,
especially with testing iron and NO3.
Color reading scales are difficult to assess.
At issue here is maintenance of nutrient levels. The
focus will be on four groups, nitrate (NO3), phosphate
(PO4), potassium (K) and the trace elements represented
by iron (Fe) in a mixture with the other trace elements. Perhaps
a better question is how close to a good range of nutrients do we
have to be in to have excellent plant growth and no algae?
Using an "estimative index" the accuracy can be as follows:
(+ or -) 5ppm of CO2 is fine in a 20-30ppm range.
(+ or -) 1ppm or so of NO3 is pretty reasonable.
(+ or -) 2ppm of K+ is pretty reasonable.
(+ or -) 0.2ppm of PO4 is pretty reasonable(?).
(+ or -) 0.1ppm of Fe is reasonable(?).
CO2 range 20-30ppm
NO3 range 5-10ppm
K+ range 20-30ppm
PO4 range 0.4-1.0ppm
Fe .5ppm or higher(?)
PO4 and Fe are two nutrients that are difficult
to assess without first assessing the other nutrients. If the NO3,
K, and CO2 are in good shape, you can add a fair amount
of these within a wide range. I have added up to almost 2ppm of
PO4 consistently week after week. The plant's response
is incredible. Adding traces has been a focus for me lately. Many
have stuck with the old standby of a residual of 0.1ppm of iron.
Well what does this residual tell us? Does it tell us what is available
to the plants? Is this enough? Does higher dose when the other nutrients
(NO3 and PO4) are present cause algae?