Backyard Aquaponics
A place to discuss aquaponics

Hi guys,
I'll start describing my system:
500 lt IBC fish tank
1 grow bed 100x120x25cm (300lt). Wet media probably 200 lt
Media expanded clay pebbles.
Water runs 15 minutes every hour using a timer.
I'm growing 2 broad beans, 1 lettuce 1 strawberry 1 pok choy.
15 trouts weighting 80ish grams each.
Current feeding 10gr daily (divided in 4 feeds)
water temperature have been quite low, between 5 and 20 degree

I've been running this system for 8 months, they cycle was completed in the first month.
Generally speaking I've seen nitrates the first month and never anymore.
With this feeding rate my ammonia and nitrites levels are always quite high, around 1ppm.
If I stop feeding ammonia and nitrites disappear within 2 days

I know 15 fishes are too many for my grow beds and I'm planning to add one more but shouldn't my current media fully support my current fish weight and feeding?

Also, why i'm not seeing any Nitrates with those few plants?

Thanks guys in advance and, very nice forum.

Maybe run your pump more often? May not be getting enough contact time to convert all the ammonia/nitrite.

It's most likely that the plants are using them right away or they are being used by something else, like algae. If the plants aren't getting enough nitrates they will start to yellow or just stop growing.

The low temps probably have something to do with the poor conversion from ammonia but they also help protect the fish against ammonia toxicity. Over time you may develop a more robust bacterial group that does better at processing with the cooler system water you currently have. Nitrite toxicity might be more of an issue and salting with sodium chloride or calcium chloride will help with this but you'll probably lose the strawberry plant if you salt. The normal rate is 1 part per thousand of sodium chloride (so 1gm per liter of water). The chloride ion competes with the nitrite ion for uptake and so gives the fish some protection against nitrite poisoning.

Are you pumping the full volume of the fish tank at least once per hour?
What's the pH of the system water?

Thanks for your replies guys

@LowCarbTNPer I tried to run the pump 24h for few days but there was no much change. Maybe I should have given it more time.

@scotty435
Plants are doing fine. They grow and they don't have signs of nutrient deficiency.
So far the fishes don't seem to mind about nitrites. I can stop feeding for a day or two and the ammonia and nitrites will disappear. That's to say that I'm looking for a more permanent solution even considering that fishes are just 80gr and they will grow eventually.
My pump is a 3000l/h and the fish tank is 500 liters. I ran the pump 15 min each hour. I'd say I'm pumping the whole volume each hour.
Ph is 6.6 to 6.8.

It's odd that you have low nitrates. But simplest solutions for the high nitrite and ammonia would seem to be:

another growbed (or some other biological filtration)

Less food and permanently hungry fish (not ideal)

or less fish.

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Based on your stocking level, yes you're a bit overstocked but I would also expect that your media beds could handle the waste. At this point I think the cool temps in the grow beds which reduce nitrification are the main culprit especially when they are below around 10 degrees C.

1ppm of ammonia at this pH and temp isn't really a problem. I'm basing that statement on the toxicity levels in the chart you'll find here - http://ibcofaquaponics.com/information/tables-and-charts/

For the nitrites, if you're not going to salt then I'd let the system hit zero then back off the feed slightly to see if the system can handle it. I'd keep doing that until I found a level that didn't cause the nitrites to be too high. I couldn't find anything on temperature effects on nitrite toxicity but I'm pretty sure there are some. On the other hand, I do think you may be pushing your luck with nitrite at this level for trout - https://www.tandfonline.com/doi/abs/10.1577/1548-8659(1974)103%3C389%3AENTIRT%3E2.0.CO%3B2

Just to recap your options so far -
- Salt
- Add filtration - another grow bed or other form of filter (takes awhile to get established so not ideal)
- Reduce feeding to levels the system can handle
- Reduce the number of fish
- Increase pump time on and/or aeration (might help with the bacteria doing the processing and the contact times) (you are already pumping enough to meet the guideline of turning over the system once per hour so I'm not really sure this will help but might be worth a go).

Thanks guys, all very informative replies.
About the low nitrates I've been doing the API test wrongly for months :-). I was shaking the 2 tubes for minutes but not the bottle n2...
The new Nitrates reeding is between 80 and 160 ppt. Which explain the algae problem. I did a 25% water change and stopped feeding and added many more plants.

Do you guys think that more plants could help getting faster ammonia and nitrite conversion?
Is it possible that high nitrates level was somehow slowing the ammonia and nitrite conversion?

I have few PVC pipes ready to use as an addition to the existing bed. Sort of NFT setup. I was just waiting to run water into them as I thought I had few nitrates so there was no much point in adding more plants.

Do I have to put media in the PVC pipes and if yes what kind of media shall I add?

That does makes sense of things... ie doing the test wrong.

Don't be too worried by those nitrate readings... the wise heads on here say it's ideal for them to be between 0 and about 40. But I've had them up around and above the 400s for extended periods - as a result of being overstocked. Fish and plants seemed to do OK regardless. I'm not sure if nitrates have much direct impact on ammonia and nitrites - I had no problems with them, even with nitrates off the charts for months at a time.

More plants will help lower your nitrates. I doubt it will make much difference to ammonia and nitrite... the relevant bacteria live on all surfaces in your system, including the plant roots. But, in most systems at least, the surface area of the plant roots is fairly trivial. if you want to lower those readings, Scotty's advice above is gold.

PVC pipes work well... particularly for leafy greens which are the plants most "hungry" for nitrate. There are various ways of setting them up. But I don't think putting media in them is wise.

NFT is one option - though I recall a debate about whether it was possible in a round pipe. I have no experience but I think you have to work out a way to wick the water up to whatever you have your plant growing in... at least until its roots are long enough. I'm sure you'll find posts on here if you search.

A number of us run our PVC pipes about a third or half full of water - a sort of modified deep water culture. At least that's the way I've been doing it for a few years now. Plants sit in small net pots (available online and at hydroponic stores) so the bottom of the pot sits in the water and the media wicks the water up to the plant roots, even when they are small seedlings.

One thing to be aware of is that the plant roots in the PVC pipes get quickly covered in fish solids - unless you have good mechanical filtration. My filtration isn't that good, so I mostly put quick growing leafy greens in the PVC pipes... I've eaten the plants by the time the roots start rotting.

You'll see my PVC pipes if you have a look at my first system thread. And there were some threads active a year or so back with detailed discussion about how it all works. Have a search for words like "not NFT" or modified DWC.