Reading the manual for the Fluval canister. Page 7 says "Be sure to position the intake tube away from any air source..... will diminish filter efficiency."

 any water change u do will take out nitrates more matter how small even a 5% will take a bit out. and if u have some algae growing that will take out more nitrates

check out the water changing part is this site it says 15% to 20% for most tank or do u think this site is bull crap nossie and is all wrong

Summertime, I am so glad you did not buy the magnum 350 canister filter...it is crap.
It is the only filter I have had trouble with cycling a tank.
The eheim worked beautifully and the fluval is wonderful but the marineland 350...what a nightmare.
I cleaned it out and added a new sleeve. It was so dirty from the previous owner and he obviously didn't clean it in a long time and was so heavy with sludge that the innner core canister totally collapsed, blew the o-ring and gaskets.  Then when I cleaned it all out added new media to the core canister and a new sleeve it spiked a a nitrite readiing even tho I have the marineland HOB 400 filter on the tank too.  Ugh I would never recommend this filter to anyone especially not to new hobbiests.
Now I will have to work like a dog not to lose any fish and get this **** nitrogen cycle back under control!!

I don't think it's all "bull crap and all wrong" but I have, through my own experience noticed that everything will work perfectly with larger water changes. And I'll repeat: especially when it comes to goldfish.

Removing "a little bit" of the nitrates aren't helping too much, because soon you need to change again when they reach 40ppm after only a few days Which is why I change half the water in my tank every time, and I can leave it alone for two weeks before the nitrates will even reach 30! It works better for ME because I am struggling with buckets, I change about 16 buckets of water every time, and that means carrying 32 buckets of 10kg before the tank is emptied and filled again.
Before you'll whine about me getting one of those siphons you can connect to the tap, I'll tell you that I sadly can't afford that for now, and I don't complain about working hard to keep the fish happy.

There are people on the forum that do the same 50% water changes and their fish thrive. So do mine And a healthy environment for them is all I care about.

Minde, I'm glad I didn't buy that one too.  So sorry you have to deal with it, but with your care your fish will be ok.  I know you'll put in the extra work to make up for a crummy filter.  Aren't you the one who once said she was getting up at night checking on her fish?  It might have been when ich struck from the plants.

Maybe you can find a new better filter on ebay...

i dont get it i love my marine land hob 350 works perfect and has no noise maybe it is a different model. they did change a few years ago.

if i was doing a 50% change weekly i would do 2 25% percent less stress on the fish but it still seems high to me.

The dreaded buckets!  We had to do that with the saltwater tank and now we are going to set up something so we can make it a little easier on us.  Hubby says we can put a piece on a hosepipe and hook it up to our utility sink to fill the tank back up, can't afford the python thing I think its called.  There are two of us doing the changes though so this should be ok for now and I already have the other siphon to take the water out with.  Not sure if you have looked into that yet Nossie.  Should be cheap enough for the hosepipe and the piece to attach it with is at Lowes or homedepot.  It won't have the switches to do both ways or to turn off but it will make it so that we don't have to carry those heavy buckets any longer. 

Fingers crossed this will work. 

Summer time, I just read through this thread and noticed your question about placement of an air stone too close to intake pipe...I am also curious about its effect on the efficiency of the filter. The only thing I can think of is that an air stone would cause an interruption of normal swirling movement within the tank This has peaked my interest as I have an air stone in the center of the tank which may be diminishing the filter function. I think I will have to move it    maybe get a few bubble bars to suction inside at the bottom on the opposite side...won't look as nice but oh well - just want everything to function properly in the end eh? Good luck!

Minde this tank is gorgeous!!!!!! Look at all your beautiful babies they are so pretty and bright orange and eeek! I just love it 

If the air diffuser is too close to the canister filter intake pipe, it will suck air into it and thus reduce its efficiency.
Also, it would cause it to make noise with the air in it!

ya i know this forum is for people to put there thoughts down u dont have to listen to me

but this part i know i am right

the more air u put in a by the good bacteria the better this is how a wet dry trickle filter works

 the is a layer of filter media to get rid of the crap detus  in the water (like all water filters) falls down to drip plate that speads the water out  then fall down in drops back down to the bio ball and pick up oxygen because the more oxygen the more good bacteria back though a pump up to your tank

so the more air the better

check out la fish guy wet dry trickle filter i u dont believe me 

Is the wet/dry filter the same thing as a canister filter? I'm new, so I'm not sure.

Anyway, my post about the air is a direct quote from the Fluval 405 instruction manual. It's mentioned twice in the instructions, one of which is in a gray box labeled "Important!".

I would think the company probably ran some tests and this is what they found.

creamkiller: Yeah, that I know, common sense since the beneficial bacteria need oxygen to live just as much as the fish do.
What I don't understand, is why you're saying this??

Lol, I don't even know what he's trying to tell me then. 

He was saying something about doing over 50% water changes was bad, I have never done water changes that big myself.  About the air bubbles and the filter, I dunno.  I have an air tube that runs across right in front of my intake of my filter.  Not sure if that is good or bad now, think I did get lost about that.  There are LOTS and LOTS of air bubbles in the tank now so it would be hard to make it where there are none near the intake of the filter (HOB).  Can someone clear that up for me? 

bel, don't worry about the HOB filter.  It's the canister filter, bubbler is too near the intake tube, it could cause your canister filter to suck in too much air and cause problems with that.  It would definately make some noise if it's a problem.

I think one just needs some empathy, common sense, some studying, and ability to reason things out, and some knowledgeable friends like on this forum, and you will have healthy and happy goldfish.

Sometimes we have a difference of opinion, which means that there is room for some error. Which is good, because I know I'm not perfect.