Lethargic goldfish

Question
Hi Thanks for responding so quickly!
Well it's good to know the sponge thingy is being helpful.
I thought the tank was a 15 galon but my husband says it's a 10 gal. (the fish is about 4.5-5''
including his very flowy tail)
As for the water temp, I just tried takeing it with a termometer (like people use for fevers) but the
water temp must be too low. Any ways the air temp in the room ranges from 56 (when we're not
home) to 68 when we are.
I replace the water every so often. When it gets low, random intervals, and when it get cloudy
(which really doesn't happen too often, but the walls behind the tank are pale green so it kinda
heightens the effect).I know i do something with it at least once a week, but as for the amount
going in and out, it varies.  
Is there ever a time when one shoud do a complete replacement of the water and clean
everything?
Other than that, the fish looks healthy, no spots, a feww scales missing, but he did get caught in
the filter tube when young (it's funny he's the only one left outof my original batch and wouldn't
have made it had my husband not rescued him)
That's all I can think of...
steen

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Followup To
Question -
Hello!
I have a 3 year old white goldfish and lately he's just been hanging out in the bottom of the tank
(a 15 gallon, no light, has a few fake plants, store baught stones). I thought maybe he was just
sleeping, but he seems to be sleepin' a lot. He does get up to eat, but hangs in the bottom an
awful lot.  The filter I use is a peguin mini (and I put a sponge in it to get some build up of
something, I dunno the aquarium place told me to do that) I don't know the PH or any thing like
that.
Any suggestions?
steen
Answer -
Hi Steen;

The sponge is to develop beneficial bacteria colonies for processing his waste. It is a very good
thing.

What is the water temperature? Has it gone down recently? They become more sluggish in cooler
water.

How often do you change water? Maybe he needs some fresh. Remove 25% of the water and
replace it. This should be done every week to 2 weeks.

What size tank is it? If he has grown too large for his tank he may just be making too many
toxins (his waste) for the filter to adequately remove them.

Does he look like he has spots, patches, or anything else that doesn't look normal? Any swelling
or eye changes? Bloated belly?

Let me know and hopefully we can figure out what's ailing the little fella.

Followups welcome.

At Your Service;
Chris Robbins  

Answer
Hi Steen;

Your tank size is just fine. The water is probably cooler and he just doesn't feel like moving much. Try more frequent water changes and see if he improves.

Actually, replacing water from evaporation isn't a "water change". This is because the dissolved organics don't evaporate with the water. They only come out when water is removed by you and replaced.

Unless there is some sort of emergency like overfeeding, a foreign substance or toxin gets in the tank or a disease, there is no need to completely change all the water. All it does is kill beneficial bacteria that keeps your tank clean and clear, and your fish healthy. Also, it will have to go through a break-in period all over again and this is stressful to the fish. Maybe that is why the other fish died? It is very common. Break-in takes 6 to 8 weeks. Soemtimes fish get very sick and die durig this time, especially with more than one fish to 10 gallons to start the tank with. Toxins from fish waste rise because the beneficial bacteria isn't developed enough to handle them.

Keep up the good work!

Followups welcome.

At Your Service;
Chris Robbins