I plan to have a 10 gallon tank because that is the minimum amount for a red tailed shark, if it grows of course i will get a bigger one. And i plan to only have 1 fish. What type of Filter is best for Freshwater and his the least expensive? I’d prefer an answer from someone who has a fresh water tank please 
Thanks a lot!
At least 15 years ago I bought a Whisper brand filter and used it for several years. My dad is using it now and as far is I know it still runs fine. It is similar to the one at the link below, which is currently on sale for $14 – not a bad price. The link is for Petco, but I’m sure it’s available at most pet stores. If you need more information on your Red Tail, see the second link.
Also, if you get this kind of filter, you don’t have to buy their refill kits every time you need to change the filter element. You can buy a large container of activated charcoal and thoroughly rinse the little filter bag and save quite a bit of money.
probably a 10 gallon water filter i say maybe 15$ if that and those are one cool fish but maybe 15$ but good luck but theres one rule u can nvr filter ur water too much though so 10-15 gallon filter should be fin at walmart good luck
References :
At least 15 years ago I bought a Whisper brand filter and used it for several years. My dad is using it now and as far is I know it still runs fine. It is similar to the one at the link below, which is currently on sale for $14 – not a bad price. The link is for Petco, but I’m sure it’s available at most pet stores. If you need more information on your Red Tail, see the second link.
Also, if you get this kind of filter, you don’t have to buy their refill kits every time you need to change the filter element. You can buy a large container of activated charcoal and thoroughly rinse the little filter bag and save quite a bit of money.
References :
http://www.petco.com/product/107131/Tetra-Whisper-PF10-Filtration-System.aspx?CoreCat=OnSiteSearch
http://www.fishlore.com/Profiles-RedTailShark.htm
http://www.liveaquaria.com/product/prod_display.cfm?c=830+888+1172&pcatid=1172
http://aqualandpetsplus.com/Shark,%20Red-Tail.htm
Both sites recommend big tanks. 10 gallons may be the absolute minimum, but any aquarium expert will tell you the bigger the better. The second link also mentions that Red-Tailed sharks are very likely to be infected with ick, so be sure to watch out for that. As for the filter, I would recommend getting a larger tank and going with an aquaclear filter. These are nice because you can customize what types of filter media you want to use. For example, if you have high nitrate problems, which you DEFINITELY will if you go with the 10 gallon tank, You can simply add some nitrate removing media to the filter. You will always want to keep the "foam" and "carbon" in the filter, but the biomax isn’t absolutely necessary. The biomax simply provides more surface area for beneficial bacteria to grow. There are other ways of doing this, such as using bioballs. I use aquaclear filters in both my saltwater (55g + 20g sump) and freshwater (75g) aquarium and I absolutely love them. Hope this helps!
References :
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=3610