Fluval E300 Low Flow Readings

I recently started noticing Low Flow alarms start to appear on my Fluval E Series heaters in my 75-gallon aquarium. I originally had just one E300 but a few weeks ago I added a second E300 to compensate for cool winter nights in the room. The two are installed right next to each other, adjacent to the return line from a Fluval 407 canister filter. I also have an air pump on a tank decoration located almost directly in front of the heaters. I did not start seeing the LF alarm until after installing the second heater, but now I am intermittently getting the alarm on both heaters.

My initial suspicion was that the filter flow rate was slowing down as I had not done a deep clean of the media since starting up the aquarium. The visual flow was still looking strong, but I took apart the filter and there was definitely a lot of waste/food visible, which I rinsed off (in tank water). After starting it back up I'm still seeing the alarms intermittently on both heaters.

This is also leading to large swings in temperature readings - I'll see the readings vary anywhere between 76 - 80 within a few minutes. Prior to installing the second heater it would stay pretty consistent within +/- one degree.

I've also tried rotating the pump return nozzle in a few different directions to see if that improves things, but no luck. Is there something about having two heaters installed in parallel that I need to account for?

I was originally going to install the second heater on the opposite side of the tank next to the filter intake, but I did not because the cord was not long enough to reach to the power strip on the other side of the cabinet. I could put it on an extension cord to get it over to the other side, if having the two heaters next to each other is an issue.

 

Ok, you are confusing the sensor by having these next to each other. All it does is measure how much time it takes for the water to heat up. If it takes too short of a time, then it triggers the low flow warning. It thinks you have stagnant water. But actually you have another heater right next by!

You will have to ignore the low flow warning, or move the second heater to the opposite side of the tank so that they don't interact with each other.

 

Okay that makes a lot of sense - so it’s using the rate of temp change to determine a low flow condition.

I’ll move it to the other side. It’s just unfortunate Fluval doesn’t put longer cords on the heaters, as I’ll have to add a small extension cord.

 

I moved the second heater over to the opposite side of the aquarium, next to the filter intake tube. It is still flashing the LF alarm though, so now I am at a loss on what to do. I've emailed Fluval customer support to see if they have any suggestions.

 

Its an annoying feature that you don’t need. The second heater is still heating up the tank quickly and fooling the ‘flow’ sensor.

Put some black tape over the display!