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Thread: Sizing systems

  1. #31
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    Re: Sizing systems

    It is common knowledge in both the aquarium hobby, and the aquaculture industry, that lack of water changes stunts fish growth. Try your own experiment keep several fish in an aquarium, and don't change water. Duplicate the aquarium, and change water. Even use tilapia, and a UV sterilizer. You will likely change your mind.

  2. #32
    Moderator urbanfarmer's Avatar
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    Re: Sizing systems

    Oh, I see. Well, I am still learning, and I will try the experiment you propose once I get some fish and post my data and observations here with pictures! But for now, I will take your word for it while doing some more research on how to combat this issue. And yes, I have seen this first hand with the comet goldfish I have been raising. The ones in the pond outdoors grow much faster than the ones in the tank indoors even though I feed the ones indoors substantially more than the outdoor ones in a big pond.

    I would like to point out that mathematically, it makes more sense to spread your water changes to as much water at any given time to be as much water volume at those given times as possible because this increases the effectiveness of the water changes.

    For instance, assuming a fixed level of concentration of pheromone in the water at variable levels of water changes:
    Given: P in units of pheromone per total volume of water

    Where X equals the number of water changes over a fixed interval of time and C(x) equals the concentration of pheromone:
    C1(x) = P x (0.9)^X
    C2(x) = P x (0.8)^(X/2)
    C3(x) = P x (0.7)^(X/3)

    We want C(x) to be the lowest, and we find that at any given value of X: C3(x) < C2(x) < C1(x)

    What I have done is model formulas that change the SAME AMOUNT OF WATER just spread over less frequent water changes. What the models indicate is that instead of changing 10% water daily, it is more efficient and less labor intensive to change the water 20% every other day, or 30% every 3rd day, etc. Of course, one must consider the effects of the water change on the rest of the biological system, but from a pure pheromone reducing perspective, that's the best solution.

  3. #33
    Moderator badflash's Avatar
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    Re: Sizing systems

    All things take time. If you have a mature ssystem with lots of hungry plants, there is no need for water changes. Just add make up water and check your chemistry. Don't over harvest plants or fish once you strike a balance.
    The best fertilizer is the farmer's shadow

  4. #34
    Moderator urbanfarmer's Avatar
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    Re: Sizing systems

    Quote Originally Posted by badflash
    All things take time. If you have a mature ssystem with lots of hungry plants, there is no need for water changes. Just add make up water and check your chemistry. Don't over harvest plants or fish once you strike a balance.
    but, what about their claims that there are eventually high concentrations of pheromones released by the fish to inhibit growth??

  5. #35
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    Re: Sizing systems

    The pheromones are a factor, but nitrate build up is a much larger factor. This is where keeping fish in tanks, and aquaponics differ. A balanced system should eliminate the need for the frequent water changes needed in aquarium raised fish, or aquacultured fish.

    The fish in you outdoor pond are likely growing better because of less nitrate concentrations. Your pond is not unlike an aquaponics system. You probably have some plants. Either intentionally planted, or some form of algae. Both will remove nitrates, and allow for better fish growth. Also the larger volume of the pond will help lower concentrations.

    If you get a test kit, and test your indoor comet tank for nitrate, you might be surprised at the nitrate levels. Under 40 is considered optimum for most tank fish.

    With my indoor tilapia in non aquaponic systems, I recently got lazy, and skimped a bit on water changes. I actually noticed that the fish became lethargic, and less aggressive at feeding time. Nitrite, and ammonia were fine, but nitrate was over 80. After a large water change, the fish were much more vigorous.

  6. #36
    Moderator badflash's Avatar
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    Re: Sizing systems

    With tilapia, the phermones seem to restrict breeding, but not growth.
    The best fertilizer is the farmer's shadow

  7. #37
    Moderator urbanfarmer's Avatar
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    Re: Sizing systems

    Quote Originally Posted by badflash
    With tilapia, the phermones seem to restrict breeding, but not growth.
    I am inclined to believe you, but I have genuinely not seen research either way. A few people here hold to the idea that it does affect the Tilapia's growth rate. I have only read studies where it affects breeding habits. However, I know some fish do release some kind of waterborne hormone, protein, or other biochemical as a survival mechanism that inhibits the growth of like species (intentionally or not). Even in the book "Tilapia: Biology, Culture, And Nutrition" he mentions (I think it was page 363) that he SUSPECTS there is some kind of waterborne substance that inhibits the growth of Tilapia at high concentrations, but makes note that he has no research to support that claim. Perhaps in the half decade since that book was published, there has been new research that might provide a reference for all of us? I don't know... but I'm hoping you do!

    The implications are pretty huge if there is a waterborne substance that Tilapia release or indirectly cause a buildup of in the system that cannot be removed by existing filtration thereby causing growth inhibitions of our fish. Agree?

  8. #38
    Moderator badflash's Avatar
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    Re: Sizing systems

    I've not seen any stunting with densities up to 1 lb of fish per 5 gallons of water. The fish definitely self limit breeding.
    The best fertilizer is the farmer's shadow

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