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PC MONITORING FROM
GLOBAL  AQUATICS
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There are always plenty of surprises when growing anything in an artificial environment, such as fish in an intensive system. So many times failures could have been predicted if only past trends could have been observed. There are two time elements, that when properly used, can go a long way to avoid catastrophes.
One is real time. This is "What is happening now?". The computer screen on the bottom serves this function. A quick glance and an operator can see a low oxygen long before the alarms go off. But the question is, "Why is it low and how long has it been that low"?
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The screen at the top shows the conditions in a tank as they were recorded over the past 24 hours. In so many systems the importance of this time element is overlooked.The disolved oxygen level should remain fairly constant with the exceptions of special events like feeding time or other usual activity around a tank. Since most feeding times are routine an operator looking at the data for the past 24 hours would expect to see the lowing of oxygen levels at these times. However, there is a limit to how long this level should remain low before the system picks the level back up. For instance, if fish are fed at 12 noon and the begining oxygen level is 6ppm and during the feeding it drops to 4ppm for a while, this is expected. But suppose it drops to below that for several hours and stays there until just before the next feeding? This is a real concern. It could be that the fish are not getting enough oxygen to properly digest the food. This would be caused by not enough oxygen entering the tank at the right time and would be noted and taken care of. So a check of the oxygen amounts entering the tank shows that the proper amount is being placed. Now what? This is where the predicibility comes in. The monitor is not fibbing. Something else must be wrong and if it is not dealt with could become tomorrows problem. Things that would have to be checked include:
| Possible Problem |
Solution |
| High BOD |
Tank needs to be flushed or diluted with clean water. Failure to do so will only make matters worse. Generally bacteria does not vacate any place where there is plenty of food. And with the oxygen dipping the fish will expell undigested food creating even more BOD. |
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Over Crowding
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When the fish were first introduced into the tank they were much smaller. The total weight of all the animals combined (Biomass) was at a level where the amount of water in the tank and the oxygen delivery system was able to handle the load. Now, the fish are bigger, eating more, and breathing more. The accumulated data is showing that the tank is having trouble supporting the oxygen at a continous safe level and either the population has to be lowered or the amount of oxygen increased. Failure to spot this problem can cause a high mortality in the event of even a tempory power outage. Plus it is also stressing the fish on a daily basis. Either lower the Biomass or increase the oxygen flow. |
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| WATER CHEMISTRY |
Prolonged flucuations in oxygen levels can also be caused by water chemistry problems such as high ammonia, nitrites, or dissolved gases. In these cases the oxygen might not just lower, it could also rise above expected levels which is another warning. For instance, assuming that the correct amount of oxygen for a given biomass is being added and that the levels were hanging at the correct level for days, and suddenly you see the dissolved levels rising during periods of inactivity. This could be a sign that nitrites or CO2 are elevated and the fish are not using the oxygen at the expected rate. Allowed to go on too long and the mortality begins to rise. If this turns out to be the case the tank needs to be flushed and the bio-filtration checked. |
These are just three things that can be gradually taking place that can affect a fish growing system. By observing good trends over a long period of time an operator can see when other adverse conditions are in the making and reverse the trend before it becomes a problem.
aquatic@iximd.com
Copyright 2000
All rights reserved
All information found throughout these pages are the exclusive property of Global Aquatics Ltd. and may not be copied or distributed without the expressed written permission from the owners of this intellectual property.
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