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Re: PAR meter design -- hydra attack!

> Date: Wed, 16 Dec 1998 13:58:20 -0800
> From: Dave Gomberg <gomberg at wcf_com>
> Subject: Re: Aquatic Plants Digest V3 #713
> At 03:51 PM 12/16/98 -0500,  Dorian McMillan asked:
> >midday sun output on a clear day is ca. 2000 micromol/m2/sec,
> >I've been told that you could probably build a PAR meter for around
> >$25--the trick is that it must be calibrated
> How about calibrating it agains midday sun output on a clear day?

The trick is getting the right spectral response. The detector doesn't
usually cover the right range, and getting stable filters to correct its
response is far from trivial. Once that is done, the source you mention
is too dependent on latitude, location, etc. to be anything but rough
order-of-magnitude in accuracy. Use a calibration lamp o/e.

> ------------------------------
> Date: Wed, 16 Dec 1998 18:32:09 -0500
> From: Sarah Maline <maline at maine_maine.edu>
> Subject: hydra attack!
> Hi all.  I started a 55 gallon Dutch-style plant aquarium in September.
> Everything is growing very well, HOWEVER, I also seem to have a very
> nice crop of hydra as well.  (I'm talking daphnia Hell!)
> All I can find for remedies are:  Potassium Permanganate; raise the temp
> to 104 for one hour, and other seemingly harmful methods.  I'm presently
> trying out a suggested remedy of using gouramis (they're ignoring the
> hydra even though I'm not feeding them anything).
> I'm very hesitant to use anything harsh for obvious reasons.  My Anubias
> barteri and Madagascar Lace are thriving beautifully right now.  
> Has anyone out there ever experienced a safe cure for hydra???

Yes. I have two that work for me.

Formalin (35% formaldehyde) applied at a rate of about 3-4 drops per 5G,
every day for 3-4 days usually does it, with no harm to fish or plants.
It is quickly absorbed by organics in the tank, so is rapidly
self-limiting in action. Daily repeats are mandatory. The dosage is from
memory, but I *think* it is correct. [Check on it before doing a big
tank of valuable specimens.]

Another way is to stop feeding any live foods for a week or two. They
starve to death without live prey, and all but the youngest of fish can
live through it, nicely (even if they don't eat dry food). It will take
slightly longer if you have resident, reproducing daphnia.

BTW, hydra are essentially harmless in any tank not used for breeding.
They *can* eat very small babies, so that is when I bother to clean them
out. In any display tank they are an interesting part of the biotope,
and I wouldn't bother with them. That's just my US$0.02.


Wright Huntley, Fremont CA, USA, 510 494-8679  huntley1 at home dot com
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