I think that the filtration design of the Fluval Spec series of aquariums is pretty ingenious – a simple overflow and filter media section that flowhttps://spec-tanks.com/wp-admin/edit.phps to the bottom of a pump section. Then an outlet tube from the pump up to the discharge nozzle into the tank. It is a setup that mimics the custom designs of larger aquariums and generally works very well.
There is one aspect of this flow pattern that can be a disadvantage and that is an area of ‘dead’ water located in the pump section. This may or may not be a problem depending on your setup. I tend to think you want to minimize areas of your aquarium, both in the display area and otherwise, that don’t have good flow.
A bigger issue for those, like myself, that want to put a heater in the pump section, is that without proper flow around the heater it will have a very hard time regulating temperature. Unless you have a separate temperature controller with a sensor in the return, most immersed heaters simply detect the water temperature around the heater and turn on and off as it senses the need for heat. By mounting the heater in the pump section, the thermostat will tend to energize, quickly heat up the water in the very small pump section, then turn off before begin able to raise the temperature in the display tank. One way to alleviate this is by putting some holes in the outlet tube.
By placing a few small diameter holes in the outlet tube that rises up from the pump, you allow water to circulate into the pump section. The water will then just flow back down into the inlet of the pump. This reduces the dead water in the pump section. It also gets more tank water flowing around the heater and will help the heater thermostat work much more accurately.
Diverting some of the flow through the use of holes in the outlet tube is also a way of reducing the display tank flow rate for those with livestock that don’t like strong current, such as Betta Fish.
How to Put Flow Holes in Your Spec Outlet Tube:
This is a very easy modification. The hardest part is a bit of planning for where and how many holes you want. I made my holes about 1/8″ in diameter and ended up making about 5 holes. Instead of aligning them straight up the side, I decided to alternate them slightly so that they pointed in different directions around the tube to flow to different corners of the pump section. I marked the planned hole locations with a marker.
There are any number of ways to cut the holes. The tube is not rigid and can be squeezed. One method I think would work would be to squeeze the tube flat and use scissors to nip away at an edge. The only thing to be careful of is to try and make the holes the same size so that flow is equal between them.
I tried using a drill bit at first and it worked ok, but left some plastic burrs that blocked flow. I finished the job off with a dremel grinding tool that was the perfect diameter.
Observations – Flow Tube Modification in Action:
I see only positives for putting a few holes in the outlet tube and can’t think of any negatives. The only possible negative would be for someone that needed the absolute highest flow rate in the display tank and didn’t want to divert any of the flow.
The operation of the heater in the pump section worked very well after modifying the outlet tube with holes. The temperature that I measured in the display section was very close to what my Hydor Theo 50 watt heater was set to.
Also, I think that there is less detritus buildup in the bottom of the filter and pump sections with the addition of these holes and the flow that they induce. The flow rate in the display section of the aquarium is still quite high even with some of the water diverted (my pump is set fully open for the highest flow) so I don’t see any detrimental effect there.