Is 1 Gram Of Dry Fish Food Per Day Too Much?

[fish farmer]

not sure if this matters I used all cycled rocks and media so all live. Maybe my rock already has all the po4 it can handle and yours still absorbs some? I dont know seems like a lot has changed in the 12-13 years I was gone but chemistry shouldnt have lol.

That is what I was thinking...my tank had bottomed out phos. It had been 1-2ppm before I started my task to bring it down, rock is 20 years old, never thought I would see the phos disappear.

 

[twentyleagues]

Some background. I am running a study with multiple small, 0.2 L aquaria. These systems are either started with live sand or inoculated with aquarium water. Sometimes, they are started with dead sand that has been treated with BioSpira to establish a community of nitrifying bacteria. They are fed daily with fish flakes, some with ammonium chloride and sodium phosphate. They all get a weekly water change of 25% or 100%. So far these little aquaria have grown nuisance algae but have failed to accumulate nitrate or phosphate. Something about these model aquaria is not right or how they are fed is “off”.

As a start to figuring out why these systems don’t accumulate nitrate, I wanted to establish that they are being fed approximately like real aquaria. I agree there will be a difference between rotting food and bacteria digestion of fish poo and ammonia, but come on, how hard can it be to generate nitrate?

I'm guessing you test before you change water? How much Algae? maybe its all being used up.

 

[exnisstech]

I feed the fish until they don’t go nuts when I add food. That little bit of slowing down is my cue to come back later with. The question about food amount is in support of an experiment.

Apologies. It would help if I read the first post

 

[Dan_P]

After seeing the picture of how much a gram of flakes is, I change my mind: that looks like a lot of food in a 40 gallon. I have no idea why you aren’t registering nutrients with 1g of food per day.

Is the food decomposing at all?

I assume the food is decomposing because nuisance algae growth is as vigorous as when I feed the same amount of nitrogen via ammonium chloride. I may have to run experiments to understand the results of my first experiment.

 

[Dan_P]

I'm guessing you test before you change water? How much Algae? maybe its all being used up.

Yes, test before the water change.

The “algae” consists of a community of cyanobacteria, diatoms, dinoflagellates and too numerous to count or identify other micro algae. I think you are right about it consuming the nutrients.

 

[Koleswrath]

I wonder what, if any, the impact of denitrifying bacteria is in these systems. Is a deep sand bed really necessary for denitrification? I've read conflicting arguments and am not sure what the current view is on porous live rock being able to support these bacteria.

 

[Dan_P]

I wonder what, if any, the impact of denitrifying bacteria is in these systems. Is a deep sand bed really necessary for denitrification? I've read conflicting arguments and am not sure what the current view is on porous live rock being able to support these bacteria.

I don’t know the range of environments denitrification can occur. I am prepared to be surprised. The sand bed I currently use is only 2 mm deep. Deeper sand beds are on the list of factors to study

I do know that every surface is coated with some sort of algae or cyanobacteria, providing a a black hole for nitrogen. We might not need to invoke denitrification for this system.

 

[BeanAnimal]

I noticed every time I feed reefroids my phosphates shoot up. Nitrates have been steady 10-15 since tank set up.

I think because it is basically freeze dried phosphate

 

[BZOFIQ]

I think thats way too much food in a 40 breeder

 

[taricha]

For context here's my food input on a good feeding day...

If I feed a cube of mysis, a cube of brine, and a pinch of flake...
mysis: 3.3g x 7.6% protein x 16% N in protein = 40mg N
brine: 3.3g x 3.7% protein x 16% N in protein = 20mg N
pinch of flake: 0.5g x 53% protein x 16% N in protein = 42mg N
Total = input of 40+20+42 = 102mg N in 260L system = 0.39 mg/L of N
if 100% of that protein N went into NH4 that'd give 0.39 x (18 mass NH4 / 14 mass N) = 0.50 ppm NH4

so a 65-70 gallon (of water) system, I feed the Nitrogen equivalent of ~1.2 g of fish flake, or ~0.7g fish flake per 40 gallons. close to your level.


Other hobbyists I've seen numbers ranged from about half of my input.
another had about twice the input of mine.
Rich Ross who describes his feeding as very heavy, has about twice the input* of mine.
* if you divide by his water volume, it's twice my input level. If you just divide by display tank volume, then he feeds 10x the food input to the display - but he has a sump system with 5x the water volume of the display. So it's both crazy huge and not that huge depending on the context of the question.

So Dan, my short answer to your question is that I don't think it's atypically large amount of input, but most won't do that input level as just fish flake.


A second part of this discussion is the fish flake makeup. My fish flake is 53% protein, when I did a bunch of digestions on it to analyze the C, N, and P levels in the flake, I came up with ~55% organic Carbon. doing the 16% N in protein, this gives a C/N mass ratio of .55/(.53*.16) = 6.5 to 1. (7.5 to 1 by moles)
A "meatier" frozen food is likely to have not as much carbon per nitrogen, so there's a little more potential for NO3 accumulation.
But if you wanted to see NO3 accumulate in your test aquaria, then simply run one in the dark - bacterial digestions of my fish flake in the dark spit out almost the total N content as ammonia over 5-10 days.

 

[Dan_P]

For context here's my food input on a good feeding day...

so a 65-70 gallon (of water) system, I feed the Nitrogen equivalent of ~1.2 g of fish flake, or ~0.7g fish flake per 40 gallons. close to your level.


Other hobbyists I've seen numbers ranged from about half of my input.
another had about twice the input of mine.
Rich Ross who describes his feeding as very heavy, has about twice the input* of mine.
* if you divide by his water volume, it's twice my input level. If you just divide by display tank volume, then he feeds 10x the food input to the display - but he has a sump system with 5x the water volume of the display. So it's both crazy huge and not that huge depending on the context of the question.

So Dan, my short answer to your question is that I don't think it's atypically large amount of input, but most won't do that input level as just fish flake.


A second part of this discussion is the fish flake makeup. My fish flake is 53% protein, when I did a bunch of digestions on it to analyze the C, N, and P levels in the flake, I came up with ~55% organic Carbon. doing the 16% N in protein, this gives a C/N mass ratio of .55/(.53*.16) = 6.5 to 1. (7.5 to 1 by moles)
A "meatier" frozen food is likely to have not as much carbon per nitrogen, so there's a little more potential for NO3 accumulation.
But if you wanted to see NO3 accumulate in your test aquaria, then simply run one in the dark - bacterial digestions of my fish flake in the dark spit out almost the total N content as ammonia over 5-10 days.

Thank for this analysis.

The lack of any sign of nitrate accumulation (and the overall yellow-gold color of the growth) is an indication to me that my model aquarium design is not duplicating larger aquaria. I am going to adjust light level (lower) and water movement (increase) in an attempt to shift the way the model behaves.