As I mentioned before : Here, this was sometimes last year I have endless problem with one of my siphon. I always though that all are identical.
Most of the time I just adjust water inflow to make it work, its working fine if its fed independently with a dedicated pump.. but once using the shared pump its always giving problem.
So finally today,, decide I have to get to the bottom of this problem. Its difficult to get at that's why all this delay in fixing it. I have to go under the growbed from within the fish tank... and that's not a nice thing to do.
As they say "a man got to do what a man got to do" ... get myself into the fish tank... and remove the siphon.
I am a bit of a camera shy,, and professionally as a teacher, I always feel that the subject we're presenting is most important and not the presenter in person.
After removing the siphon then I realised that the failed one (on left) is not of the same design that I normally use. I wonder why was that... it must be a Sunday when I assembled it where I ran out of parts and all shops closed. At lease that what I told myself... to make it OK for this blunder.
As photo above the fail siphon use threaded coupling instead of the tank adapter that I normally use for my standard design on the right.
There is a slight difference in its inner diameter between the two as shown below. The failed siphon using threaded adapter is slightly smaller inner diameter as compared to the one on the right. This slight difference make it behave differently hence require slightly different water inflow setting to the other siphon.
What prompt me to check it is that while I am cleaning the siphon with a bottle brush, I feel restricted in pushing the brush into the failed siphon. This is the first indication to me that its not identical to the rest. Its been quite a while since I last cleaned it, and all this while I just adjust water inflow to make it good.
Finally its fixed .. :)