Can anyone give me some reassurance or advice; We have a 70 litre fish tank with one fancy and one common goldfish. For a while now the fancy goldfish has been spending a lot of time on his back. I have changed their diet from flakes to pellets and he has made an incredible recovery! However, since they have gone to pellets, the tank smells - not fishy, just yucky. I've got the test kit that checks the PH level, ammonia, nitrate and nitrites and all are absolutely fine. I carry out a 25% water change once a fortnight and test regularly, but that smell is still there! I'm assuming it has something to do with the pellet food, but is there anything I need to be doing to combat it or should I just live with it?

Thanks for any help!

How much pellet do you give them? I don't quite know what the smell could be. I'll have a quick search on the net and get back to you.

Hmm I get the feeling it'll only come up with feeding. What filter (internal or ext) do you have and how often do you clean it?

Do you have a lot or any plants or algae? That can give off an earthy smell.

They are the smallest pellets because the common goldfish struggled with larger ones. I try to give them 2 pellets each twice a day, but confess that I might slip a couple of extra ones in with every feed - they're so darn small!

It's an internal filter and I clean it once a fortnight. It's quite a big filter and seems to work quite efficiently.

This is a smell - sort of like rotting vegetables, but there are no live plants in there as the common goldfish likes to eat them. The smell dissipates as soon as you take the tank lid off. Water changes don't really help.

Don't get me wrong, it's not the worst smell in the world, it's just really odd that it's only started since changing their food so I am concerned I'm over-feeding them.

you are doing everything right that you have said so far. have you got sand or gravel in there? is it like a rotten egg smell?
what food is it that you are feeding? aquarian or golden sinkers or another?

*Heidi*

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Hmm you seem to be on top of it all then. I don't feed pellets only frozen blister pack foods bloodworm and the like. My dad bought some bloodworm pellets for them but the fish weren't impressed and left them they are quite messy. But as you say your only feeding them a small amount. Why not try frozen? The pellets do tend to stink more than the frozen.

Thanks for that! I do have some frozen food, but I'm not sure how to use them! Everything I buy from our local aquarium seems to be Japanese! I have some frozen square of these things which were once squirming around like little maggots, but I'm not sure what they're called (I'm such a novice but learning fast and really enjoying it!)

lol it's ok, just defrost them in a bowl an hour or so before due to feed. I'd say about half a square if they are standard sized about 12 to a pack. As you don't have that many fish to feed on them and you don't want to clog your filter. The average rule is enough to feed on for 5 minutes. To be honest I think five minutes is a long time i'd say about 2/3 but you know their feeding habits better than I do

They would be bloodworm, lol! They tend to be the best for them, the most liked. Just drop a block in(or half a block if they are bigger) and it will defrost in the tank, it wont hurt. Or you could defrost it in some water and drop it in.
Would the food be Hikari? which is Japanese?
The reason I ask about the gravel or sand is because if it is sand, anaerobic bacteria can build up in it and change Nitrate into free nitrogen(thats good) or they can change it into nitrous oxide(i think its called, can never be sure) and that gives you a rotten egg smell. the trick is to keep stiring the sand on a very regular basis or to change to gravel.

*Heidi*

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Yes to all of the above! I have to admit that I drop our frozen food in straight from the packet and it does no harm but it does suggest defrost first.

I'm assuming it's gravel as sand isn't suitable as far as I know for tropicals