Aquaculture in the Classroom

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Re: Tilapia and the use of NaCl

From: Gordon J. Mengel, Special Projects Director/Aquacultue, The Council
Date: 02 Feb 1999
Time: 11:16:03
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Question: We have heard that the use of NaCl or salt will help with high nitrite levels and also aid in helping to prevent diseases. Is this true?

Response: Yes, NaCl helps reduce the threat of nitrite toxicity, it relieves stress, it reduces incidence of fungal infection, and it reduces the energy required by fish to perform active transport of materials across cell membranes.

Question: We have a four hundred gallon tank with about 70 tilapia that are 1-2 inches long. How much salt should be added if any.

Response: Since the fish a very small, I assume that you are just getting started. First of all, within the first couple weeks of operation, you can expect the nitrite level to "peak." This is normal as your biofilter comes "on-line, " that is as the filter media is colonized by nitrifying bacteria. By the second or third week of operation, as the Nitrobacter spp. bacteria multiply and convert more nitrite into nitrate, you can expect the nitrite level to decrease and the nitrate levels to rise.

As long as you do not over-feed and the conditions are kept optimal for the biofilter to function properly, you shouldn't expect to have any further increases in nitrite. However, it is a good idea to continue to monitor nitrite (weekly) and chloride levels. This can be done chemically with a Hach or Lamotte test kit. Optimally, you want the chloride level to be at least 6 X's the nitrite level (ex. if nitrite is 3 ppm, then chloride should be at least 18 ppm). The critical level is at about a 3:1 chloride to nitrite level. If you need to raise the chloride level, then you should add NaCl at 2.5 oz. per 10,000 gallons to raise the level 1 ppm (for your tank this would be 1 oz. NaCl per 400 gallons).

Good luck with a great endeavor! And, thanks for sharing your question with everyone. If there's anything else, drop us a line.

Gordon J. Mengel The Council

Last changed: February 02, 1999