Goldfish and 29 gal aquarium

Question
Wow!  I didn't realize that goldfish grow so large!  So must I eventually get a larger tank and if so, when would be the best time to do that and what size?  
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Followup To
Question -
I have two goldfish, one is about 6" tip to tail, one is about 4" and also one 3" algae eater.  I did have a Moore that just died this past weekend (he was about 5" long).  My aquarium is 29 gallons, I wondered if it would be okay to get a replacement fish or if I should just leave it as my present three fishes?  I don't have $$ to buy a larger tank so that is out.  Help!
Answer -
Hi Amy;

I think the 3 you have now are a safe population because they are all going to grow even more too. Goldfish get 6 to 8 inches each and algae eaters get anywhere from 6 to 12 inches depending on the type. The measurements don't count their tails so they still have quite a bit of growing to do. You will hear of a 'rule of thumb' that says "one inch of fish per gallon", but  this is only for fish that stay small (3 inches or so). Goldfish can't be stocked that way. They are deep-bodied messy fish that need more space to thrive than little fish do.

Be sure to change water often with those guys too. Replace 25% of the water every week and vacuum the gravel every 2 to 4 weeks to keep them happy and healthy.

At Your Service;
Chris Robbins

Answer
Hi Amy;

Most people don't know that they get so big. The real tough part is that they are so messy too, even for their size.

I really think the tank they have now is fine for them to reach adult size. You just don't want to add any more to it. Keep up with weekly 25% water changes and gravel vacuuming every 2 to 4 weeks, don't overfeed, and it should work out just fine.

If you want more fish, get a 55 to 70 gallon and add extra filtration. Canister filters are great. Get two that are each what your size tank needs to give your fish double filtration. You could add a couple more goldfish that way. Just stay away from Koi. They get 3 feet long.....yikes!

At Your Service;
Chris Robbins