I've had an eheim classic as well and loved it for my 120g but while I was away nobody maintained it and it burnt out completely. To be honest no matter what filter you use your nitrates would still be the same. The few ways to remove nitrates from a tank is water changes, plants (the faster growing the better), or setting up a nitrate reactor. The nitrate reactor is basically a home for another type of bacteria that breaks down nitrate, but buying a reactor is pricey and often unnecessary with proper water changes. Most people who have one, have very large tanks where water changes would be more extreme than a 55g. Plants use them to grow but since axolotls like it cold don't expect plants to be growing fast enough to remove all the nitrates produced. Canister filters are great at mechanical filtration and removing suspended particles. All the different media options allows you to keep the water looking crystal clear and can provide a good home for the bacteria you need but requires cleaning to remove the waste it collects which as you know can be a pain. The water will still contain nitrates though. On top of that axolotls produce heavy turds that stay on the bottom until cleaned. They have great gravel vacuums that allows you to attach directly to a sink to make water changes very easy. I used to do that at home with my 120g. Basically it sucks out the waste and however much water you want, then you turn on the sink (make sure its the same temperature!) to add water. You can add your water treatment directly to the tank without fear of it killing your cycle. Just add a little bit more then the estimated gallons being replaced.
I'm thinking of turning my Hydor Prime 10 into a 'nitrate reactor'. All you need to do is get some appropriate media (Seachem Denitrate) and create an anaerobic environment, such as by using a very low flow rate filter (Hydor Prime 10). I'm still using it to filter my 3ft tank, but if I do convert it into a reactor then I'll post the results as I'm sure people would be interested in permanently reducing nitrates to 0 for £40 (Hydor Prime 10 + Seachem DeNitrate).
I already have an adapter that connects a hose to a bathroom tap so I used some more hose adapters to make a venturi that will initiate the syphon from my tank to the sink. Now all my water changes are automatic and I just sit back and watch the tank drain, before removing the venture to fill it up again. Whole think cost me about £5. I can post the details on how to make it if people are interested.
I'm curious, how do people manage to filter the bigger tanks, while keeping the water movement low enough for axolotls? My tank is filled to 185L so I need a 740LPH circulation rate to filter the water. But with the Fluval 306 (which had a circulation rate of 780LPH), I had to turn it down to half the output (even with a spray bar) to stop the axolotls gills from blustering about, and they haven't emerged from their hides much since moving in.
I also chose to order a Hydor Prime 30 as it was going cheap as hell on amazon. I never realised how important the self-priming feature of the Hydor Prime range is, until I used a filter without it.
I'll see how the Hydor Prime 30 is on the noise front, since it's a pretty heft 25W motor. The only other canister I was considering was the Hydor Professional 250, it's the same media volume as the Hydor Prime 30 but with baskets, zero bypass, and a more efficient (and possibly quieter) motor.
I don't know why Hydor are not as popular as they should be; they're one of the only companies to give you a completely honest figure for the flow rate, filters are very reasonably priced, quiet and well engineered, and their customer service is fantastic. You get an actual person responding to your questions and not just a drone reading off the FAQ list.
Based on my experience, I'd recommend that anyone in the market for a external filter go for the Hydor Prime range. Right now the Prime 10, and 30 are £32 and £44 on amazon. Way cheaper than any comparable filter and the self-priming means you'll never have to suffer a rattling impeller.
