A Community and Forum For Aquaponic Gardeners
How many fish do I need?
Our system is 2 months old. We have a 3 bed/1 fish tank IBC system outdoors in TX. Harold was awesome in helping us with cycling the system (since we had 3 freezes between April and May that kept sending our biofilter back into hibernation!). Yet now, instead of too high numbers, we can't seem to get any! The biofilter is working overtime and the plant growth over the last two weeks has been tremendously crazy.
Our problem is now this....the system cannot keep up with the nitrate demands of our plants. Our daily readings are 0 Ammonia, 0 Nitrites and 0 Nitrates. Our pH is around 6.3-6.5. The iron is about 1ppm. I am feeding the fish three times a day. We have 10 6-8in tilapia and 22 2in tilapia. Even an hour after feeding, I'm barely seeing ammonia at .1ppm.
How many fish do we need to provide enough nitrates for the plant? Is there even a way to determine if there is a deficiency?
Our tomato plants are showing yellow lower branches at the same time that they are flowering. They have also grown 8 inches in 10 days. The reason that we were thinking that it was a nitrate deficiency was that our lettuce and other plants were also experiencing yellowing. Our zucchini are not growing (though I think that's more of an issue of non-pollination than anything else) and our beans and peas are growing.
Do we need more fish?
Replies to This Discussion
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Permalink Reply by George on
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It's a bit of a dilemma. If you increase stocking, then you must have the necessary aeration. Your plants are now heavy feeders but fall/winter plants are not so much. Fish grow, so possibly you will need to reduce their numbers at some point if you become overstocked. Rules of thumb might help.
Increasing fish is an option.
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Permalink Reply by Jonathan Kadish NYC AA Chair on
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How many grams of fish food are you feeding a day?
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I'll have to measure tomorrow. I normally just throw in what they eat in a few minutes plus a few more (and if they eat that, I increase the amount I feed them the next day).
Is there a formula for how much feed equals how much nitrogen?
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Well there are a couple of things to mention... First your nice looking system is very young and your first couple of crops won't be your best. Aquaponics continues to develop for up to 2 years. You will see your yield continue to improve over this time. The best be is not to over manage the results... they will come.
Your grow beds really don't need a lot of fish poo to thrive. You would need to feed 10 - 20 grams of food per square meter of grow bed. If you were doing DWC it is 60-100 grams because you are removing all the solids in filtration. Again it will take time for your system to be rich in nutrients so be patient. Don't expect fruiting plants like tomatoes or peppers to do well until 6 to 9 months out. Early on things like lettuce, basil, bok choi are going to do ok.
Also, here is a guide of deficiencies to look out for
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Permalink Reply by Carl on
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Thanks for that image. That'll be useful.
Jonathan Kadish NYC AA Chair said:... Also, here is a guide of deficiencies to look out for
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Ok, lets just say that weighing fish feed was an interesting experience this morning. It was harder to visualize how much I usually give them. Totally misjudged and they got a nice big breakfast this morning :) I think the usual is about 10g of feed for the fish. If I manage to feed them 3x, I'm looking at around 30g/day.
In looking at this chart, it looks like it might be magnesium deficiency, not nitrogen, that we are dealing with. Something to research today :)
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You could ad some Epsom Salts ... couldn't hurt.
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How do you determine how much Epsom salts to add?
I wish there was a tool that would figure all the calculations and tell you what to add when :)
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I have read that for a quick remedy you can apply a foliar spray with about 1-1/2-2 teaspoons per litre
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Thanks. I think I'll do that tomorrow - if our garden is still here. Threat of tornadoes tonight into tomorrow has me a little stressed (can you tell I didn't grow up in the Midwest?!).
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Good question. after watching Nate's videos on iron a couple of times, I've begun adding epsom salts weekly at about the same rate as iron EDDHa). Not sure if that is the right amount but possibly someone else has an opinion on the subject.
Beth Medeiros said:How do you determine how much Epsom salts to add?
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Permalink Reply by Vlad Jovanovic on
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George, When you say "at about the same rate as iron..." do you mean by weight of the powder/salt, or by percentage of iron/magnesium contained in the powder/salt?
Epsom salt (or magnesium sulfate heptahydrate... MgSO4-7H2O...is about 9.98% magnesium...we'll just call it 10% from here on out)...
I'm not saying don't add the epsom salt, just be aware that all of the base/metal cations (like Mg, Zn, K, Ca, Cu, etc...) behave antagonistically toward one another. Meaning too much of one will block the uptake of one or more of the others. Iron is the only plant essential element that does not seem to exhibit this antagonistic behavior (within reason)...so you have a ton of leeway with iron...but not so with Mg and the other metal cations...so be aware of that. This is not my opinion or anything, it is a very, very well documented, and long known phenomenon...
Since it's still all about balance...It might be very prudent to add a combination of salts (2 parts KCl to 2parts NaCl to 1 part MgSO4) at a rate of 500ppm and then just leave it alone for the next 6 months and just feed your fish (and add iron as needed of coarse). For the NaCl, use pure unadulterated dehydrated seawater. (The above ratio takes into account both the Mg as well as K content of the sea salt)...It is a safe pretty generic, low level "one size fits all" type ratio (you could easily double the amount to 1ppt and have no problems...used just once that year, not weekly, not monthly, but yearly)..."
...how much magnesium to add..." ...pretty much depends on what you are growing...since say, things like cucurbits (zucchini, cucumbers, squash, melons etc...) need A LOT more Mg and K than things like peas, beans,hot peppers, basil, lettuce etc...'way' more than even tomatoes...So the above 3 salts at the prescribed ratio should help cover many of those bases without messing up you light feeding plants...plus the chloride ions act as a soothing tonic for the fish...it's win/win (unless you are growing stripped bass they apparently have a peculiar sensitivity to K)...
George said:Good question. after watching Nate's videos on iron a couple of times, I've begun adding epsom salts weekly at about the same rate as iron EDDHa). Not sure if that is the right amount but possibly someone else has an opinion on the subject.
Beth Medeiros said:How do you determine how much Epsom salts to add?
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