[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Phosphate remover and CO2 rates

On Thu, 15 Jan 1998, Matthew Mason wrote:

> 1.  Does anyone know the mineral/product name associated with phosphate
> removers; i.e., scientific or common name.  I have heard it called xeolite
> but do not think that this is possible since it is a silicate which is a
> negatively charged molecule attracting positively charged ions.

Zeolite is a class of mineral used for softening water.  The actual 
product used these days is probably synthetic, rather than the natural 

I don't know for sure, but I think that the commercial phosphate remover 
I once used was just porous, anhydrous aluminum hydroxide.  It adsorbs 
more than just phosphate.

> 2.  Has anyone experimented with "home-made" phosphate removers?  And are
> these rechargable as so many of the store brands are?

I haven't heard of anyone trying it.  The one I used was not particularly
rechargable, despite its advertising.  It adsorbed enough organics to turn
from pure white to dingy tan.  I think that ideally you could bake those
organics off and recover at least part of the initial capacity.   


As to CO2 intake and loss rates, here are three calculations.  There's a
lot of estimates in this, but you might find it interesting, just the

1) The bubbles from my DIY CO2 setup are small - about 90 per cc.  At 200
bubbles per minute (about the average, I think) I get 2.22 cc of CO2 per
minute or 133 cc per hour - the same as 0.133 liters per hour.  Using the
ideal gas law, that means it's producing about 239 milligrams per hour. 
Most (but not all) of that dissolves. 

2) If the limiting C fixation rate is about 2,000 nmoles/square
meter/second, then plants should be able to fix up to 29.37 mg CO2/square
foot/hour.  The area of plant surface that might be ingesting CO2 is tough
to estimate.  Let's say that the entire floor area is covered with leaves
receiving direct light, and both sides of the leaves can adsorb CO2.  My
55 gallon tank has a 4 square foot floor area, so the tank contains about
8 square feet of effective plant surface area.  The maximum CO2 fixation
rate in that tank would be about 235 mg/hour.  I assume this will happen 
only while the lights are on.  Leaves receiving only indirect light can 
also contribute to CO2 fixation, so this approach could underestimate the 
maximum rate.

3) I try to keep the plant population in the 55 gallon tank about
constant.  To do that I trim about enough every week to fill a small salad
bowl.  I think that's about 0.2 lbs (91 grams) per week, moist weight.  If
the plants are 6% carbon (85% water, carbon 40% of dry weight), then
they're fixing (and I'm removing) about 5.5 grams of carbon/week.  The
lights in that tank are on 12 hours/day, or 84 hours/week, so the carbon
fixation rate is about 65 milligrams/hour of light.  The corresponding CO2
fixation rate is 240 milligrams of CO2/hour. 

So it looks like the plants in this tank are probably growing about as
fast as they can, and while the lights are on the plants are using CO2 as
fast as I can add it - there's not much left over to lose.  The lights are
only on 12 hours a day, so up to half of all the CO2 added is lost to the
atmosphere while the lights are off.  CO2 is also generated in the tank by
respiration and most of that amount is also lost to the atmosphere.

Roger Miller