Filter Media swap results in 50% flow rate loss?

[charrold]

This is a little esoteric, so bear with me. I am a longtime member, but generally read and lurk, however, if anyone knows the answer to this question they are on this forum.

I have a DIY filter setup with custom made 150 liter barrels. The first barrel is mechanical and the second 2 are bio. I recycled last year's franken-filter mechanical filter media (foam pads) when I first got the new barrels and started the filter this spring. I know that my flow rate with those media pads was somewhere around 300L per minute (plus or minus the margin of error of the flow-rate meters - 3% give or take).

I decided that now that the fish are more active, the weather is somewhat warmer (In the northern part of the NL), I should probably replace the old pads with shiny new ones. (They were pretty worn and flattened from the pressure in the new mechanical tank) I got the following to replace what I was using:

2 - 5CM Coarse
1 - 5CM Medium
2 - 2CM Fine

so about 12CM all in which was about what I had before, minus the aforementioned flattening.

I will explain the full setup if anyone cares, but upon this change, I noticed immediately that the flow rate in the waterfall return was MUCH lower then before the replacement, and indeed the flow meters are showing an average of 160L/Min now versus 300 before. The question is this:

Would nice, new, tight-fitting pads really cut the flow rate in half? Pond is still clear, numbers are still good, and it still rolls over the ~10k liter pond in around 60-90 minutes if my math is good, but the flow rate drop seems really harsh - anyone got experience with this?

 

[charrold]

Yeah. Turns out I am dumb and physics is not. I sealed the mechanical barrel before turning on the pump, trapping a massive bubble of air at the top of the chamber. This, of course, resulted in the water pressure being *just enough* to squeeze out a trickle of water past the air pressure.

Popped the top, started the pumps with the filter lid on loosely to bleed the air, and low and behold! Flow rate backup to 300/350 LPM.

Physics 1
Me 0

Lesson learned. Might install a breather in the top of that chamber one day to not have to deal with this, but the head hight on my pump is pretty gnarly so it would be like one oof those UHF antennas... Maybe a breather valve in the outflow. Ah well, back to tinkering...

 

[JRS]

Glad you found the problem, thanks for the update.