A land-based closed-loop tilapia farm in British Columbia, Canada was struggling with fish health due to insufficient pH control and accumulation of nitrogen-based contaminants in the water system. To address the problem the farm installed a membrane bioreactor (MBR) system to maintain low levels of contaminants.
They used hydrated lime (Ca(OH)2) for pH control, which was very labor intensive, caused plugging of feed lines, and did not effectively control pH – especially when the fish were being fed. As a result, nitrate levels in the water were reaching a danger point for the fish. In addition, they were needing to supplement with table salt (NaCl) in order to keep a healthy protective slime layer on the fish bodies.
This study provides data on how the replacement of lime with a magnesium hydroxide-based product resulted in strong pH control and nitrogen reduction, along with dramatic improvements in water clarity and fish health. The nonhazardous liquid product, called AMALGAM-30, did not require operator maintenance, providing reliable, steady feed for optimum pH and alkalinity control. After three weeks of operation the nitrate levels in the water system were reduced by 89% and the water clarity (turbidity) was dramatically improved. They stopped supplementing with sodium chloride.
Perhaps the most dramatic observation from this study was the overall improvement in the health of the fish. The protective slime layer on the tilapia improved greatly when the feed of lime and table salt was replaced with AMALGAM-30, with noticeably less cuts and abrasions on the fish. The improvement in health was so noticeable that they received numerous comments from buyers about the improved fish quality and dramatically improved water clarity. As a result, the farm has completely discontinued the use of lime and salt, and has installed a permanent AMALGAM-30 storage and feed system.