NetMax wrote:
"Derek Benson" wrote in message
...

On Wed, 20 Jul 2005 02:46:05 -0400, Logic316
wrote:


Hi folks,

I use activated carbon in a power filter for my aquarium. I probably
don't really need it since I do 20% water changes each week anyway, but
I like to have the water as free of impurities as possible and it does
seem to make it smell cleaner :-) I'm interested in knowing how to tell
exactly when a batch of activated carbon has absorbed as much organic
waste as it can hold and has reached the end of it's lifespan. I
regularly change it every month, but I don't like having to guess as the
stuff is probably still good and I'm wasting money and effort and
throwing away whatever beneficial bacteria has gathered on the granules.

I'd also like to know if it can be easily cleaned and recharged. I read
in a few places that the absorbed waste material can be separated from
the carbon by baking it at a high temperature but I can't find the
details of the process. Can it be done in my oven at home? Also, is it
possible that by tapping and breaking the carbon granules with a mallet
you can expose fresh unused areas of the carbon and extend it's life
that way?

Thanks for any tips!

Peter Hunnam writes in his book that to reactivate the carbon you need
to bake it at 500C (932F) in the absence of oxygen. So you probably
can't do this at home.

He also suggests that you can add a few drops of Methylene blue to the
intake of your filter; if the carbon is exhausted you will see a blue
color in the water returning from the filter.

-Derek


To add to the information, some filters (many HOBs) move the water too
quickly past the carbon for the meth. blue test to be really representative,
so with some models, don't be surprised to see fresh carbon fail this
particular test method. The working life expectancy of carbon really
depends on the quality/condition of the water, so filtering RO or municipal
water will give very different results. In the trade, we use 3 weeks as a
reasonable life expectancy for home filtration system, and 6 to 12 months
for commercial systems. That was interesting about the 500C bake requiring
an absence of oxygen (not that I would have tried it anyways ;~).


With oxygen, you get a pile of ash and some CO2 rather than carbon. ;-)
To keep adding to the info, high temperature is how carbon for aquaria
should be activated in the first place. Cheap carbon is sometimes
activated with strong phosphoric acid instead and leaches phosphates
into the tank water. One of the first things to check in a tank with
high phosphates is the carbon (put a few granules into a sensitive
phosphate test set up with distilled water).

Good carbon should already have its pores exposed to water, so breaking
the granules with a hammer will only get you a mess.

--
Elaine T __
http://eethomp.com/fish.html '__
rec.aquaria.* FAQ http://faq.thekrib.com