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[APD] Re: Changing GH

Eric Wahlig said:
<<The Seachem Flourish Tabs contain about 20% calcium
and less than 0.1% magnesium. I don't think they are
contributing much to your rising GH. The most likely
reason for this is your top-off water. You didn't say
if you used tap water for this but if you do then you
are slowly increasing the GH, and probably the KH
also. The water that evaporates has no minerals in it;
they are left in the tank, but the water you replace
it with (your tap water) has minerals in it. The net
effect is a small but continuous increase in hardness.
Relatively large, say 50%, regularly scheduled water
changes will gradually bring it back down to the same
level as your tap water.

As far as plants go that consume large amounts of
calcium and magnesium; I can recommend the fast
growers that generally come from harder waters, like
Anacharis and Valisineria, would do a good job. The
real way to control and stabilize the hardness though
is through regularly scheduled water changes of a set
volume of water. Your tap water, at 8 dGH, sounds
excellent for growing plants. >>


Yes I do top off with tap water. And I leave the lid
open so the water temp stays below 80F, so there's
lots of evaporation going on.

I actually started topping off with distlled water at
the end of July to see if I could stabilize the gH. I
also did water changes using distilled water during
the texas algal bloom for I guess two weeks - I don't
know what chemicals the water department uses to
control the algae, but the water department claims
they're "safe". Yeah, whatever. I regularly change 2-3
gallons of my 12 gallon tank every week. I've noticed
that since that time I've been adding distilled water,
the gH rose 2 degrees, and the kH dropped one degree,
so now it's at 3 degrees. So if I keep doing this, my
pH will become unstable. Grrr.

I still wonder why the gH keeps going up if I'm
topping of with distilled water! 

Also, aren't both calcium and magesium components of
water hardness?

Other details:
My tank is 12 gallons, low light tank 
I use flourish as the substrate, so I guess no
limestone or shells (re: Wright's reply)
I have 5 crypts, 1 Compact sword and 3 struggling
vallisneria (they stopped dying off since I added the
I also have a pothos plant hanging out of the lid so
only the roots are in the water. (It was originally
sitting in the window in a glass vase, the roots had
developed an algae problem so I stuck it in the tank
for the otos to snack on.)
No Co2 added.
The only crustacean is a single ghost shrimp. 

I guess biogenic decalcification would be bad as it
causes pH to rise, no? 

Maybe I'll try as you suggested - 50% water changes
using tap water.

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