Oliver
10-23-2012, 12:43 PM
It has been a while since I've updated the "Aquaponics 101" posts. As we have built and tested additional configurations, adjusted the amount of food given the fish after doing some accurate food weight measurements and having the occasion to measure the fish weight I've concluded that some of the information given was less than optimal. In fact, it was pretty far off.
Once we realized that we were not feeding the Tilapia in our systems the optimal 1.5% per pound of fish per day for maximum growth rate we made that adjustment. It showed us that the previous 3 gallons of deep media bio-filter/grow bed per pound of fish was about twice what the system could handle. The real number is more like 6 gallons of media per pound of fish when fed the optimal amount of food for fast growth.
This comes back to the idea of being able to use the grow beds to break down the solid fish wastes. As indicated in the "Improving Water Quality" post, the solid fish waste pose a problem in the bio-filter if allowed to accumulate faster than can be broken down. In that post I showed an additional mineralization tank to aid in this solid fish waste breakdown process. That system is in place in our grow room but not in our greenhouse which has a similar sized aquaponics system.
What we were really doing in the greenhouse was supporting a very slow growth of the Tilapia, which meant we were feeding them about half the optimal amount of food for fast growth.
As a result of this new information I have changed the numbers in the "Aquaponics 101" posts to better indicate what we would have experienced if we had fewer number of fish and feeding them the optimal 1.5% per pound per day of food.
I have also changed the optimal pH numbers after watching the pH swing and the water chemistry changes follow along numerous times. I now realize that an even higher pH is required for optimal bacteria waste conversion. The new number is a system pH between 7.0 and 7.6. Every time the pH dropped below 7.0, the ammonia levels started to climb and the visible water quality deteriorated.
Oliver
Once we realized that we were not feeding the Tilapia in our systems the optimal 1.5% per pound of fish per day for maximum growth rate we made that adjustment. It showed us that the previous 3 gallons of deep media bio-filter/grow bed per pound of fish was about twice what the system could handle. The real number is more like 6 gallons of media per pound of fish when fed the optimal amount of food for fast growth.
This comes back to the idea of being able to use the grow beds to break down the solid fish wastes. As indicated in the "Improving Water Quality" post, the solid fish waste pose a problem in the bio-filter if allowed to accumulate faster than can be broken down. In that post I showed an additional mineralization tank to aid in this solid fish waste breakdown process. That system is in place in our grow room but not in our greenhouse which has a similar sized aquaponics system.
What we were really doing in the greenhouse was supporting a very slow growth of the Tilapia, which meant we were feeding them about half the optimal amount of food for fast growth.
As a result of this new information I have changed the numbers in the "Aquaponics 101" posts to better indicate what we would have experienced if we had fewer number of fish and feeding them the optimal 1.5% per pound per day of food.
I have also changed the optimal pH numbers after watching the pH swing and the water chemistry changes follow along numerous times. I now realize that an even higher pH is required for optimal bacteria waste conversion. The new number is a system pH between 7.0 and 7.6. Every time the pH dropped below 7.0, the ammonia levels started to climb and the visible water quality deteriorated.
Oliver