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Re: Crushed Coral, KH, GH

Rachel wrote:

> My willow hygro (H. salicifolia) is
> growing these ugly, stunted, twisted leaves, and from what I've read I am
> thinking it might be a calcium deficiency.

That does sound like a calcium deficiency.  I've found that giant hygro
(H. corymbosa, I think) is fairly sensitive to calcium deficiency so it
isn't that much of a stretch to believe that willow hygro by be
sensitive as well.

A lack of boron can cause similar problems.  There might be other
possibilities as well.

I treat calcium problems in my giant hygro by pushing half of a 600-mg
calcium tablet into the substrate at the base of the plant.  If the
deficiency hasn't advanced too far then the plant will produce new,
underformed leaves in three or four days.  If the deficiency is advanced
then the growing tip of the plant may have died and the plant will
branch and grow healthy leaves from a joint further down the stem.  That
might take more than a week.

> My pH is 6.8 due to bottled CO2, and my Kh is 3.5. I'd tell you my GH but
> I'm pretty sure my test kit is bad - it's an Aquarium Pharm. kit and rather
> than turning orange and green it sort of stays yellow or clear. I had tested
> the water earlier when the kit seemed to be working and GH was about 5.

Calcium is part of the GH.  In fact it is usually the larger part of the
GH, so that if you have more than a couple degrees of GH then you should
have enough calcium.  If the GH is less than a couple degrees or so then
you still aren't necessarily going to have a problem, depending on what
else is in the water.

High sodium levels in conjunction with low GH will trigger calcium
deficiency. Another problem is that while GH is usually mostly calcium
there are a few places where it isn't.  In that case your plants can get
calcium deficiency problems even when there is a substantial amount of
hardness present.  The relatively high magnesium levels (compared to
calcium) might block plants' ability to take in calcium.  Neither of
these problems are common.

> I tried putting crushed coral in; it raised my KH to 5.5. I can keep the pH
> at 6.8 by turning up the CO2, but the cardinal tetras in there would rather
> not have the GH too high. So here's my questions (and thanks for reading
> this far!): does crushed coral raise GH as well, and does it raise it in the
> same proportion as it raises KH? If so, is there something I can put in the
> filter to raise KH only, and if there is a calcium deficiency, will raising
> the KH only solve the problem?

Crushed coral will raise both GH and KH.  Calcium is part of the GH.  KH
does not measure calcium in any way, so raising the KH doesn't do you
any good.  

I can think of two possibilities.  Perhaps you have a boron deficiency,
in which case you might read past posts on dosing with boron.  However,
be careful when dosing boron, as it is toxic to some plants at rather
low levels. The other possibility is that your water contains quite a
bit of magnesium (which is also measured as part of the GH) but only a
small amount of calcium. For a fairly high price you can get hardness
kits that measure let you determine how much of that is from calcium and
how much is from magnesium.

Personally, I'd just stick a calcium tablet in the substrate.

Roger Miller