FLOW RATE, HOW MUCH IS ENOUGH

From AlCOAST WEB SITE 7-1-02

I saw some posts on bait tank fill time so knowing that it is just about the time when this question starts coming up in the form of numerous phone calls I think this might answer some questions.

Question: "Hey, my bait doesn't seem to last too long, how fast should my tank take to fill."  That question has several answers and explanations.  If I could invent a bait tank that would fill in 3 seconds and have no turbulence I would have done it, but a 3 second fill time would create something like a Jacuzzi effect. Way back when I heard that if you fill a tank too fast you can over oxygenate the water.  If anyone ever tells you that look them straight in the eye and tell them they are full of it.  Oxygen or O2 is held in water and measured by its saturation level.  This is the amount of O2 that can saturate in water, or become soluble in water.  The saturation level is normally measured in PPM (parts per million) and as a percentage.  The saturation level for O2 in freshwater at 80F is approx. 8.1ppm at sea level.  At higher altitudes, it decreases.  The best you can do is to reach 100% O2 saturation -- to get more O2 requires a pressurized reactor.

If you are fishing in water that is say 70% saturated you will never exceed that 70% no matter how much water you pump through the tank as long as the saturation level stays the same.  What is important though is turbulence, current, direction and pressure.  Although turbulence or too strong a current in a tank is not desirable, neither is depleted oxygen (O2) content nor the build up of ammonium from fish excretions.  Why I would love a tank that filled in 3 seconds with no turbulence, pressure and had good direction with minimal pressure is that the tank would stay crystal clear, O2 levels would never fall and ammonium (fish excisions) would be non existent.  Of course this is not possible so we settle for what is.  I get asked the question "how fast should I fill the tank that I just made.  My answer on a home made tank is normally 7 to 8 1/2 min., yet on a Kodiak or Aqua World tank I will recommend 4 to 6 min with 3 min not really a problem except with very weak bait.  The difference is the Kodiak Tank uses a full baffle system and the aqua world tank has a series of holes in which water can flow into the tank vs a single inlet fitting used mostly on home made tanks.  The single inlet fitting produces a high pressure spot that will descale some bait and if positioned at the bottom it will stir up the scales and debris that normally settle to the bottom.  The Kodiak Baffled system is also directional in that the slots are cut at an angle to provide for a directional water flow or current over the water column of the tank.  Most Fiberglass tanks also provide a baffled inlet but are not directionally cut. 

Cold water holds more O2 than hot water so when you head south toward Baja where it is not unusual to have water above 87 degrees in the summer increase your flow but be cautious of turbulence and pressure as hot water also produces bait that is not as hardy, lethargic and loses scales faster than bait in cold water.  One way to control the flow on your tank is to simply add an inline PVC ball valve.  I tend to stay away from using marine washdown valves such as the chrome brass ones most boat mfgs use as they are very restrictive with small port openings and definitely don't use the little garden hose splitters or ball valves that have the little  (3/4" long) handle sold at the home and garden stores.  The opening in the ball is less than 3/8" on most of them.

So next time you turn on your bait pump check out your fill time.  It is the time from the moment you turn on your pump to the time that your overflow outlet starts to run water out of it.  If it is way to slow check for kinked hoses and restrictive water fittings or you may have to go to the next size pump.  If all else fails and you still can't keep a chovie alive by the time you hit the breakwater maybe you should stick with plastics, (kidding).  The easiest way to find out is ask the boaters at the ramp at the end of the day how there bait did and go from there.  This time of the year the water starts to get warmer,
the bait is never allowed time to cure as it is sold faster than they can catch it and the dines grow to gigantic proportions.  Some days you can't keep it alive no matter what you do.

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