How much NO3 and PO4 do you feed in a day? (Plug in your feeding and find out)

[taricha]

So, what is your lowest limit of detection for bio-mass?

If I had a new tank, I probably wouldn't notice the first several hundred grams of biomass as biofilms on all surfaces. But in a tank set up for many years, biofilm probably isn't getting thicker one week to the next, So i can look at how softies added polyps and sump algae added mass - which I can see from one week to another.

Would you estimate 1 lb of bio-mass if a pound of bio-mass was smeared evenly over your aquarium surfaces? On average, amongst friends, how much nitrogen in ppm of nitrate is needed for a pound of bio-mass?

I did a similar exercise once.
Using very very rough math I got daily chaeto export numbers for N and P that were the same order of magnitude as my N & P food inputs.
I used data from the "Down the Drain" article on exports that gives the numbers for wet weight caulerpa.



and here's what 30g of wet weight chaeto looks like. I remember reading somewhere that chaeto is on the 90% water end of the scale.

so you'd need over 3 times that much to get to 100g wet - 10g dry weight.

So if I feed 1 cube of mysis + 1 cube of something else, I get a daily food input of around
40-55mg N, and 2.5-5.5mg P
0.7-0.9ppm NO3 and 0.03-0.06ppm PO4

This seems reasonable to me because my exports average around 30g chaetomorpha a day, which if the numbers are around those cited for caulerpa here, then I'm exporting about 30mg of N and 2.4mg of P per day through chaeto. So it might be very wrong but nice to see the food inputs and algae exports around the same scale.

 

[Dan_P]

If I had a new tank, I probably wouldn't notice the first several hundred grams of biomass as biofilms on all surfaces. But in a tank set up for many years, biofilm probably isn't getting thicker one week to the next, So i can look at how softies added polyps and sump algae added mass - which I can see from one week to another.

Clearly explained. Thanks.

When we export nitrate by carbon dosing…did you ever confirm that the amount of bacteria mass, the films we see and what is collected in filters, is approximately or seems like the correct amount?

 

[taricha]

When we export nitrate by carbon dosing…did you ever confirm that the amount of bacteria mass, the films we see and what is collected in filters, is approximately or seems like the correct amount?

I'm not confident in that at all.
Sometimes - if we are doing high doses of carbon that cause cloudy-water blooms, then yes. The bacteria in those cloudy-water events can be measured to have plausible biomass numbers for C N P. (once did digestions on cloudy water from carbon dose in lakewater and the NO3 and PO4 that went missing from the filterable water was found in the filtered out bacterial biomass.)
So yeah - if it's a big enough dose to make a cloudy bloom, then yes. But for the more common smaller doses of carbon - the amount that becomes biomass vs the amount oxidized for energy probably varies a lot by carbon source, and at small doses - it might not even feed mostly bacteria at all (lots of things that aren't bacteria eat acetate).

 

[Dan_P]

Thanks @taricha

So, carbon dosing can result in a lower nitrate level but for a given aquarium, predicting the dosing rate to see a nitrate drop may not be possible. On the other hand, aquaculture business seems to be able to predict the necessary carbon to nitrogen ratio in feed to keep nitrate at a minimum. I wonder if that provides us a lead as to why hobby aquaria have unpredictable carbon requirements. Not sure how to study this on a small scale.

 

[taricha]

On the other hand, aquaculture business seems to be able to predict the necessary carbon to nitrogen ratio in feed to keep nitrate at a minimum. I wonder if that provides us a lead as to why hobby aquaria have unpredictable carbon requirements.

My hunch is that if we each had a liter container of bubbled salt water with 100ppm NO3 and a few ppm PO4 (PO4 in excess, I mean) we could probably predict an amount of ethanol needed to cut the NO3 in half to 50ppm, and I think our predictions might hold up well.

But tell me we want to lower NO3 from 10ppm to 5ppm in a reef tank with < 0.05ppm PO4 (not necessarily excess) - then I have not much confidence in being able to predict how much ethanol it'd take.

(Being able to estimate the background feeding input for a reef tank in NO3 and PO4 - as in this thread - might help somewhat in lowering the number of confounding unknowns.)

 

[Dan_P]

My hunch is that if we each had a liter container of bubbled salt water with 100ppm NO3 and a few ppm PO4 (PO4 in excess, I mean) we could probably predict an amount of ethanol needed to cut the NO3 in half to 50ppm, and I think our predictions might hold up well.

But tell me we want to lower NO3 from 10ppm to 5ppm in a reef tank with < 0.05ppm PO4 (not necessarily excess) - then I have not much confidence in being able to predict how much ethanol it'd take.

(Being able to estimate the background feeding input for a reef tank in NO3 and PO4 - as in this thread - might help somewhat in lowering the number of confounding unknowns.)

I can see studying carbon dosing with either a pelagic approach, carbon dosing one liter of aquarium water, and with a benthic approach, dosing carbon to surfaces removed from the aquarium, such as sand, rocks, pieces of tubing and pipes and microscope slides that have been submerged a few weeks.. The latter approach would need the water tested for activity and subtracted from the total. In both approaches, the effect of light would need to be studied.