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degrees of hardness is useless



IMHO all these hardness measures are just plain confusing and nearly
useless.

Traditionally folks used the hardness kits to estimate water suitability
for fish and later the same measurements were applied to aquatic plant
husbandry. These are archaic measurements. What you REALLY want to know
is the concentration of calcium, magnesium and potassium in your water.
You can get those figures from your water utility usually or you can
dose your water change water with a specific amount of a more
concentrated solution. Sure you can ESTIMATE the amount of minerals in
your water but you will not know how much of each mineral is present.
Potassium in particular is NOT measured at all.

10 parts per million seems to be adequate for potassium and magnesium
however calcium seems to be used or absorbed in greater amounts so I
would suggest something like 50 ppm of Ca in your water. If you have
more than that, don't panic; its ok. Those amounts of nutrients dosed in
the water change water should be sufficient for 2 to 4 weeks given a 25%
water change ratio. 

This is educated guess work based on my own experiences. If someone can
estimate the amount of plant mass which can be harvested in a specified
time under ideal growing conditions, we could refine the nutrient use
estimates. Not all the nutrients are used by fish; snails absorb and use
calcium for example and I suspect that the fish might use some too.
-- 
Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!