Hi,
I have a Hagen Marina i110 filter in my 54L tank which has been there since the tank set-up in mid-October. It doesn't seem to circulate the water surface much, if at all, although it definitely has a strong 'waterfall' like effect immediately in front of the filter. I haven't changed the cartridge yet as I don't want to risk losing the good bacteria when the tank is still relatively immature. Therefore, I'm thinking of reincarnating my goldfish's (RIP) first filter - a Clearjet 1 (which, from recollection, only housed sponge) - and having this as a second filter.
Also, thinking ahead, I notice that the cartridges contain carbon and zeolite
http://www.rakuten.co.uk/shop/aquapet/product/A134/ , and from recollection from my goldfish-keeping days, ought to be removed if adding medication. Then, if the tank should need to be medicated at any point, the Hagen Marina i110 could be removed, or the Clearjet 1 transferred into another tank and it set up as a quarantine tank (I have an old, slightly smaller tank which could be set up for this purpose if/when the need arises).
My thoughts are:
(1) to add the Clearjet 1 with some sponge firstly into the 54L tank, in addition to the Hagen Marina i110 filter, and that hopefully after some time (how long?), this Clearjet 1 filter would then be considered 'cycled'. Is this counted as a "fish-in cycle" or not, given that there's an existing filter already in there ie do I need to take extra precautions to ensure that all is well (or am I putting the fish at risk in any way), and would I need to do more frequent water changes than my current 20% weekend changes involving siphoning and 10% mid-week non-siphoning changes? (Sometimes I just do a 20% change with siphoning every 5 days rather than a weekend water change and a mid-week mini water change.)
(2) once the Clearjet 1 is fully cycled, to replace the Hagen Marina i110 cartridge, which might improve its water circulation on the surface of the tank. Would the replacement of that cartridge then count as a new "fish-in cycle", requiring extra precautions, etc.
It's possible that, once all the above is done, given the extra filtration, I may consider adding a third and final shoal of fish which would bring me up to full stocking capacity.
Does this sound sensible enough? Also, would I be correct in thinking that if the Clearjet 1 were fully cycled, then a QT could be set up on an as-needed basis ie immediately as the need arose by simply transferring across the filter and some of the water from the main tank?
Sorry for the long posting. Everything has been going well so far with my 6 x-ray tetras and 6 pygmy cories, and I want to keep it that way! Many thanks.