Hehe it's one of those mykegonlegs light green coloured bottles. I bought it when I bought the keg system from the HB shop.
Poida,
I'll assume that you actually inspected your pickup tube and you don't have ancient hop matter or a bug in there adding flavour to your beer enroute to the glass! When you've carbonated your beer, does it quickly go flat after a day or two without re-gassing - ie, you don't have a leaky pressure relief valve or wanky lid that's creating a micro sized airgap / slow leak? Have you pulled the tap apart, cleaned it out and sanitised before re-use?
Is the light green coloured bottle all CO2, or pubmix / nitrogen?
Whatever it is, and I'm assuming that it's happening in all kegs, not just one, then you need to consider what's common and go through a process of elimination. Without being rude, are you sure you have your brewday procedure and hygiene protocols all ok? Are you using fresh ingredients? Do you check the smell and taste of your yeast starters to ensure you haven't got stressed / mutated / autolysed yeast?
Are your grains fresh? Do you have mouldy hops? Some off flavours take time to manifest themselves and you might be blaming the kegs for something that started several days ago and only appears on your flavour / taste threshold once the beer's in the keg...
Do you rinse your kegs out before you rack beer into them? Are you using a cleaner that's leaving microscopic pits in the surface of the keg interior - eg strong bleach left to soak in kegs overnight or longer is a no-no...And while were at it, are the insides of the kegs clear of scars, pitting, marks, rust etc?
If it were me, I'd check everything that comes into contact with the wort after the boil and see if the HBS will swap your gas bottle for another one - it's not a big deal and they should be just as keen to help a customer as you are to solve your problem.
Cheers,
TL