Decreasing Flow With Maxi-jet Powerheads?

[dilbert]

Hi all,

I bought yesterday a third Maxi-Jet MJ500 powerhead for my 15 gallons tank.

I noted then that the two first ones which are in use about three months had a weaker output. I cleaned both the older ones by cleaning the impeller and every gunk in there.

After cleaning, the older powerheads weren't remarkably stronger. Every powerhead seems to have a different output. The newest powerhead is the strongest one, but the older ones have a different output, too.

Can someone explain this?

And is there a simple method to measure the output like putting it on the bottom of a bucket and measure the time it empties that bucket or so?

 

[5teady_2012]

Strange question but, maybe the coils on the magnets get worn and this causes them to get weaker over a peroid of time, i know what you mean though cos i have 2 identical powerheads and 1 is a lot stronger than the other.

 

[dilbert]

Unfortunately, I didn't compare the first two ones when I bought them new but from memory I have the impression that the weakest one now was stronger before.

But when something gets worn in only three months how will this end up then?

 

[5teady_2012]

That i cant answer m8, if you think its getting bad then take it back to where you got it from..

My lfs always signs my box and the box is your garauntee, thats what i would do.

 

[dilbert]

That i cant answer m8, if you think its getting bad then take it back to where you got it from..

My lfs always signs my box and the box is your garauntee, thats what i would do.

There are two points with this.

At first, the LFS where I bought the third powerhead (Interfish in Ossett) did say they wouldn't take any powerheads back as I especially ask for that. That was the reason to buy again a Maxi-Jet as the two others I have are really quiet and that's what is really important to me.
I don't know now how would react Pet&Garden World in Leeds where I bought the first two ones. At least they are working. A wise guy could could come up with that the slowest one meets the specified 480 l/h and the faster one would exceed it.
I got also another small powerhead from Haileda that would fit perfectly but is really somewhat noisy. Fish People in Keighley sold it to me assuring it were absolutely quiet.
I still have an occassional use for those unwanted powerheads and don't mind if that kind of crap doesn't pile up more.

At second, my main concern is, how different are all these powerheads from each other and would I have to test them monthly and return them all again and again?

I mean as you say yours are different and mine are different, so that's until now 100% of powerheads that all have a significantly different output. As other people don't respond I don't know if they aren't aware of this problem or don't care or have the impression or are even sure that identical powerheads have the same output. Maybe I should start a poll.

 

[SkiFletch]

Are all inlet strainers the same and are all clean?

 

[dilbert]

All inlet strainers are identical and the rest of the pumps, too.

I cleaned thoroughly the inlet strainers and the impellers and the surrounding openings as well. It looked to me that cleaning didn't improve much what makes sense. If not it would have been a cumbersome design where you would need to clean the impeller every few weeks.

I can imagine that the pumps won't be exactly 480 l/h +- 1 l/h but the subjective feeling is that the output of the weakest one is 50% less than that of the strongest one.

I'm only concerned because rearranging those pumps and adjusting the right flow for every corner and different critters is always a pain. If it would be only streaming water against the live rock I wouldn't care really.

 

[SkiFletch]

Well you can always bucket-stopwatch test them to see what their flowrate is like Objectively. Wish I could be more help