Excessive fish waste good for plant?

[carpguy]

Plants need some source of nitrogen. Ammonia/ammonium or nitrates are both usable and the fish are one source. You may or may not need to supplement. Fish food can also be a source for phosphates, not really sure about how much remains in the fish poo after digestion. There may be some other stuff, not really sure.

There is an approach that includes overfeeding the fish to feed the plants but there are a lot of other elements to it and it seems to not be mix and match. For a higher light CO2 driven tank you'll need to address ferts, although the fish and their food are part of the whole equation.

 

[mogurnda]

Just to clear up a few things. Keep in mind that a fish is not a nuclear reactor, so if an element goes in, it comes out. Phosporous goes into the fish in several forms, and comes out mostly as inorganic phosphate (PO4). Iron comes out more slowly, and usually in the poo itself, but will be available to the plants eventually. One reason to keep some of the mulm around.
The fish do the plants a favor by taking proteins and nucleic acids from food and breaking them down into forms, such as CO2, NH3, NO3 and PO4, that are easily utilized. Well, some plants don't particularly like NO3, but that's another story.
Carpguy makes an important point about the balance between light, CO2, NO3, and PO4, plus minerals such as Fe and Mn. In a non-injected tank, usually CO2 limits the amount of plant growth, but if you're injecting enough CO2, then something else will limit growth. If you really want to know whether your plants are getting enough NO3 and PO4 from poo, use a test kit. I bet you'll have plenty from all those fish

 

[isaac newton]

mogurnda thx for your responce, i found it quite informative.. When fish take in food, what elements/nutrients do they attain??? You say that iron nitrates etc are dispursed in the waste, then what do the fish take in?

 

[carpguy]

Fish take in things like protein and give off things like ammonia. Take in sugars and give off CO2, etc. Lots of things go in and either 1) stay in the fish 2) change chemically 3) don't do 1 or 2. The chemicals that make up the fish (and the plants) come from the food (or from fertilizers, or from fertilizer that comes from fish food using one route or another). Other chemicals are metabolized and take part in chemical reactions that changes their characteristics. Your fish aren't eating ammonia pellets, they're eating protein pellets which later on becomes ammonia -- the nitrogen remains nitrogen but the molecules aren't the same molecules. Adding sugar to the tank isn't the same as adding CO2, even though both contain carbon and oxygen.

Everyone who keeps fish in a planted tank uses fish waste to fertilize the plants. Most (?) also use supplemental fertilizers, lights and CO2 to help the plants. You can provide good conditions for your plants while simultaneously providing healthy conditions for your fish.

There are people who take a low-tech approach and rely on fish waste and other decomposing organic water like extra fish food, plant matter, etc. Diane Walstad's book describes this approach in detail. It isn't a simple hands-free-look-at-it-go approach and it doesn't include high light, supplemental CO2, or massively overstocking your tank (you're not anywhere near a borderline).

HTH

 

[mogurnda]

You say that iron nitrates etc are dispursed in the waste, then what do the fish take in?

You can think of it like the fish are a temporary holding facility. When food goes in, it is used to make structural proteins, enzymes, nucleic acids, and all of the stuff that makes a fish, although some stuff goes right through. Minerals such as iron, manganese, magnesium, etc are generally used in small quanitities in enzymes. Almost all of these are "turned over" with old proteins, for example, being broken down into ammonia and CO2 and being replaced by new ones. Sugars and fats are used as energy, and stored and burned as needed. The specific reactions fill books, but the point is that food is made of dead animals, which contains most of what plants need to grow. Fish, and bacteria turn it into something that can be easily absorbed by the plant.

Carpguy, I hope I didn't sound like I was advocating dumping food and hoping for the best. Maybe I should have been explicit in saying that, with a population like isaac's, I didn't expect a shortage of NO3 and PO4, but that it can be easily tested. Then there are trace elements and minerals he can spend his time worrying about.

My message was mostly in response to what I read as a few unclear statements about biochemistry.