Hi Eyring & Bigjim. Thanks for your replies. I don't think either explain my problem.
Eyering...as I said, it is a new powerhead (including the impeller). The old one did the same thing. So unless the design of the impeller is causing the bubbles to form then it can't be the cause otherwise everyone using Juwel powerheads would have the same problem.
Bigjim....There seems to be different opinions on biological sponges. I started out leaving them to go bio on the advice of one of the guys at my LFS
. A few months later I has phosphates building up and spoke to a different guy at the same LFS
. He asked about my filter media and advised that I DO NOT allow the sponges to go bio and wash them weekly in tap water then rinse in RO
water. I read up on this issue and there is a split in opinion. The reason for not letting them go bio is given that they become a nitrate trap....I dunno how....but this is what the second guy at my LFS
said as well. There are arguments for both on these forums....I have read a few. So that is why I don't let them stay in for more than a week. As for washing them leaving bubbles...I don't think so. Firstly they are too course to trap any air. Secondly...they are at the bottom of the filter box and if I aggitate the top media (charcoal sock) a bit the bubble shower increases dramatically which indicates to me the bubbles are in the upper layers of filter media and are released when I move it. that is why I was wondering if the chemical process within the charcoal reacting with something in the water could produce bubbles. BTW...I have even tried soaking my charcoal in hot water before using it to remove trapped bubbles in it...makes no difference.
Thanks both for your ideas.
Any more ideas .... anyone?