Sean Peck of Knoxville, Tennessee shared this great Fluval Spec video with us via the Fluval Facebook page. Check it out!
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25.06.11 / 2am
HEATER PLACEMENT WARNING!!!
I think the SPEC is a great little tank and I want to get one for myself.
However, I have read a number of of posts by owners who have created heater / heating problems for themselves with this tank by their placement of the heater in the pump sump chamber of the filter. The heater was placed here to maintain the clean appearance of the tank. Unfortunately, this sump has to fill and drain from the bottom for the filter system to function. This traps a small volume of water around the heater which heats quickly and then turns the heater off. This behavior prevents the aquarium from heating properly. Even increasing the heater size from 10 watts to 100 watts will not raise the aquarium temperature appreciably, it will just reduce the “on” time of the heater – this ratio of “on” time to “off” time is called the duty cycle.
Fortunately, there is a simple solution to the problem. Just drill a 5/64″ hole near the top of the translucent pump discharge tube. This will mix the heated water with the filter flow and allow the heater to function properly.
Calculation Basis Of Hole Size
Using the filter flow rate data for the Fluval SPEC and data from the sump pump supplier’s web site, I estimated the pump has a discharge head of 35 cm of water at a flow rate of 40 gallons per hour (gph). The orifice flow calculation with a flow constant of .62 and the head of 35 cm of water for a 5/64″ (.0781 inch) hole is 4.69 gph. This is the internal flow from the top of the pump sump to the bottom and, with a 10 watt heater, will result in a 0.87 degree F rise in the pump sump relative to the tank and filter.
Note that the filter system total flow will be reduced by less than 2 gph since there is sufficient pump capacity and most of the system pressure loss is in the elbow and discharge nozzle which are downstream of the orifice.
If anyone has any questions, just post them here and I’ll try to answer them.
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