Backyard Aquaponics
A place to discuss aquaponics

I have a home built system that's been running successfully for several years. I never changed any water, just added water from time to time, and grew varied vegetables and herbs successfully. While I've had issues with mold and aphids in the past, thanks to help from this forum I was able to get those issues under control with a USB-powered fan and white oil, respectively.. so thanks!

However, recently the system developed a strong sulphur smell that's suffused our house and made my wife understandably quite annoyed. I tested my water with my home test kit and found that while the ammonia levels were in the "ideal" zone, chlorine was safe, and ph was 6.2-6.3, the nitrate levels are through the roof (200ppm).

My working theory is that my five goldfish just got too large for the tank (about 20 gallons of fresh water) and the system hit some sort of tipping point where the bacteria just can't keep up with the fish poop. When one fish died, I tried for the first time changing out most of the water. This helped the sulphur smell go away for a while, but in two weeks it was back. Another water change, and it's back again.

The design of the system is very simple: it's an ebb and flow on a timer, with draining effected by suction through the same latex tube that floods the bed every few hours. It's got the usual german clay pellets for the bed. I've been able to grow basil, mint, tomatoes, bamboo quite successfully (although lettuces and beans always die). It's got a growlight that's on during daylight hours (that also runs the fan).

What do people think: have I just outgrown the capacity of the beneficial bacteria that served so well and for so long, or is something else at work here? My wife wants me to kill off my fish and get new ones (because who will take huge goldfish?) but I feel bad just killing the beasts, it's not their fault they grew. I've tried putting them on a diet of only 2-3 feedings/week but that hasn't helped much.

Thanks for any ideas/feedback!

How many fish do you have? Never mind, just saw the number - 5 goldfish. You might be approaching the limits of what the media can do - here are some basic guidelines on fish stocking - http://www.backyardaquaponics.com/forum/viewtopic.php?f=12&t=6646

The setup might have less smell by increasing the number of cycles on the flood and drain or switch to using a constant flood system where the wet gravel and fish tank walls aren't getting exposed all the time.

It looks like you're only using a portion of the volume in the containers and it's tough to tell but I think you may be wetting the top layer of media in the grow bed - if you can keep the top dry there will be less evaporation and potentially less smell. Putting in a standpipe would allow you to adjust this and would overflow right down into the fish tank for aeration. You probably have room to increase the amount of media which would give you more filtration for the fish (might not be enough but it would help)

FWIW - I had a pretty good sized indoor system for a couple of years without any odor problems (150 gallon tank) but I also had adequate filtration so if none of this works either increase the filtration or give some fish to a friend.

Thank you very much scotty435. I think you also helped me with mold the last time around.
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On this go-round, your input gives me a lot of food for thought. My rig only has about 3" of grow bed. It floods nearly above the top of the grow-bed, but I can certainly add more grow-bed and not flood to the very top surface. I have a standpipe, but it was cut higher than the grow-bed and intended only for emergencies like the timer is mis-programmed (by me) and flooding goes on for too long. If I just raise the grow-bed so that it covers the standpipe, and flood for long enough to have an exit out the standpipe, maybe I can get to the happy state you're suggesting.

Some related q's:

* Isn't important for the water to drain out regularly though to avoid problem with rotting roots?
* The growbed I'm using (hydroton: https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1) is pretty expensive, but that was the best option 3 years ago. Are there good cheaper alternatives these days I could reach for ? (for instance what about this coco peat stuff: https://smile.amazon.com/General-Hydrop ... ments=p_85)

I guess you're asking about Constant Flood here. With CF the water is always being pumped and falling back into the fish tank - with all the movement the water is getting aerated and the roots get plenty of oxygen so they don't rot (kind of like a river). The only time the water isn't moving is when there is a power outage. By keeping the water in the bed during a power outage you prevent big fluctuations to the water level in the fish tank and have more water in the system overall - but yes for really extended power outages it could cause some plant health problems (the effects will be minimal with a day long outage except you'll want backup aeration for the fish).

The one thing you should watch for with any system is excessive accumulation of solids in the grow bed because these are your biofilter and it won't work the way it's supposed to. Basically it becomes anaerobic/anoxic and you get some funky odors and root rot. That may be what's going on for your system if the fish load is too high.



I'd stick with the expanded clay. I think it's still the best option if you can afford it and it's the easiest to work with. Expanded shale would be my second choice and Scoria would be third - it will work pretty well but it's not as light, rough on your hands and needs to be cleaned pretty well before use. Other types of rock and media will work but make certain you avoid anything with calcium carbonate because that will raise the pH of your system and cause nutrient lockout problems.

Coco peat will work but it is organic and will eventually break down. I'm not certain how good it would work as a biofilter media in the grow bed and I'd be more likely to use it in a wicking bed which isn't really what you need in this case because you do need biofiltration.

Sulfur smell is usually from anaerobic breakdown. My guess would be that you have accumulated enough fish poop somewhere that's preventing the water from staying oxygenated.

Try cleaning growbed media and any poop that might have settled elsewhere in low flow areas of your system.

Are there compost worms in your gb? They might help break down the poop and keep things aerated (by crawling through it). If there aren't any, I recommend adding some.

Thanks to both scotty435 and scott_dc for your excellent advice.

@scott_dc, there aren't compost worms but I will get some. WOuldn't they drown in constant flood though? Also if I clean the gb would that have the effect of eliminating the beneficial bacteria?

Your bacteria is on all surfaces , tank walls , pipes ect so clean out of your grow bed wont hurt.

Bad smells as said above is likely a "Dead" zone from fish waste and or large rotting plant root mass , gas is produced by unwanted bacteria

Clean out and worms in

If your system gets overloaded simple fix is to trap some of the fish waste before it gets to the growbed

Run water onto a piece of coarse foam (aquarium shops have it) perhaps every other day what ever works

Thank you @Terra, that's really helpful!