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Do tilapia produce more odor in indoor systems?

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I raise tilapia and other species in indoor recirculating systems in my basement. This year it's been much cooler than normal outside so I haven't removed them from their winter indoor tank and liberated them into my outdoor ponds for weed control yet. The other day the wife and I noticed the house smelled and I traced it to the tilapia tank in the basement. 

I don't believe I've had this issue with my other species or it may be a matter of the fish load in the tilapia tank which is quite high. 

Did a major water change of both my basement tanks (other tank has black crappie and bluegills) and cleaned the respective filters although I clean the mechanical filters on a weekly basis.  Odor has gone away at least for the time being.  

Edited by Cecil (see edit history)
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  • 6 months later...

@Cecil I have raised tilapia indoors and find the smells go up when O2 goes down. I ran a biofloc this summer that had 75 fish in 55 gallon tank with nothing other than a sieve to remove biomass to dry and feed back to the fish. It was a very interesting way to grow tilapia. No filters, no mbbr just a sieve. It worked very well but it stunk. I had to be very constant on the carbon input to keep ammonia down with no mbbr. I will not do that one indoors again until I build another barn. I do not understand the water changes. Why do you change the water out? I only change water out when sterilizing a system to restart? What type of mechanical filters do you use?




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Thanks for the reply. It's definitely a possibility that oxygen goes down as the fish load increases. 

The system I use for the fish other than the trout hatching and rearing consists of a circular tank with a bottom center drain that I can pull a knife gate valve on the floor to flush any wastes around it due to the diffuser mounted above the bottom drain that pushes water up and down the sides of the circular tank and back to the drain area. My solids filter consists of a 55 gallon blue drum packed with netting that captures solids via a 2 inch PVC siphon into it from the fish tank which of course runs continuously. A small mag drive pump that sits on top of the filler material pumps water to another 55 gallon blue drum (moving bed  biofilter), which consists of a membrane diffuser in the bottom center that constantly moves plastic media up the center of the drum back down the sides. This overflows back into the fish tank to complete the cycle. 

I change about 50 gallons of water whenever I drain the solids filter drum to facilitate hosing off fish wastes off of the netting. Depending on the fish load and size his can be as little as once a week to once every few days. 

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HI Cecil & Joe,

Odor, oxygen, bio-load, filtration and water changes are all complexly linked together.

Odor is caused by anaerobic bacteria buildup. The odor is one of their resultant waste products. (as is CO2 and ammonia)
Causes can be infrequent/no water changes, little/no supplemental aeration, high bio-load and/or feed rates -v's- low(er) volume (bio-capacity) systems.

Oxygen is consumed not only by the fish, but by aerobic bacteria... in fact, the bacteria can be more demanding than the fish, in some systems/water/feed rate ratio's.
Oxygen saturation is directly linked to CO2 saturation, as one increases - the other decreases.
As feed rates, bio-loads, fish size/waste increase so does the increase/build up of CO2 production.... as does the demand on oxygen by both, the fish and bacteria.

Supplemental aeration and filtration are implemented to address oxygen demand, CO2, feed rate, bio-load.

However, this does not address, filter, dissipate, desolve or neutralise several/many other properties that build up and/or reduce with time, or bio-load.
These include the reduction of water stability and buffering capacity via consumed minerals, sodiums, calciums etc... and include build up of disolved inorganics, proteins and pheromones.

Pheromones play a key factor in over all growth, maturity, fertility, hatch rate & FCR (feed conversion ratio).
The only way to reduce pheromones is water changes, I believe.
I have read nothing to suggest that plant growth results in a reduction of pheromone concentrations, as it does ammonia, nitrite, nitrates, phosphate, iron reductions... etc.


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Toga we have been playing with electrolysis to remove hormones from the rosenburgii tanks in several trials to find away to decrease aggression and increase stocking densities. The funny thing was that the electrolysis seems to remove NH4 at a good rate as well as create chlorine but this is easily delt with by a mixing tank. I can talk more about this but I do not want to hijack anyone's thread. I agree that the bio load is what gets smelly.

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That is very interesting, Joe.

Rosenburgii & ERW ?

Are you sure you are not my twin ? lols

I'll start a new thread later today re Electrolysis.
As it happens, I too am experimenting with ERW (electrically reduced water)

What's in a name, ehh ?


Edited by Toga
spelling - of course (see edit history)
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  • 2 weeks later...


we just faced the same problem. We never had within 5 years much trouble with smell but as we extended our system and the fact that crayfish demand too much space we introduced tilapia to boost our Nitrate need. Our experience is that Tilapia is much more dirty than crays and they were smelling until we battered the tanks with Oxygen. (Using an air blower) As we experienced sufficient oxygen supply was the A&O the smell disappeared as fast it came. 

There are options with pure oxygen (from Bottles) supply but they are in Thailand (one of the main producer of Tilapia) not recommended. The Farmers told me the fish gets "brown Blood" but also they told me that you can be gentle with normal air supply as it doesn't harm the fish. 

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