I know this is a very old topic but beginners still read it.
"Not True" on so many filters ! Which one do I choose ?
A better statement would be " So Few Adequate filter's out there for turtles when homework is done !
If people read more than a one page basic care sheet they would understand what's needed for most turtle species . Then there are those who place money on what they buy because that small cute baby is small. They do grow , large, females larger than males lots of them up to 12" and some even bigger like cooters. Only a very few are adequate for a turtle please read below.
The 10 gallons of water for every inch of shell is not just for more swimming room But for you to be able to control the waters parameters for a cycled tank which will help you keep it clean so your filter can do it's job. Filters are sold as fish gallons and turtles are messy so need 2-5x's the flow of fish so : a baby needs 2x's flow of fish , juveniles need 3-4x's flow and adults 4-5x's flow with the needed amount of water to maintain a cycle. The 5x's is for larger adult female's.
Much info out there on cycling here's just one :
https://aquariuminfo.org/cycling.html Media that comes with filters are mostly for fish adjust for a turtle read here : viewtopic.php?f=9&t=30145
Turtle's get big and live a long time , the initial startup cost can cost a lot. Males can get 9" depending on it's DNA needing 90 gallons water alone. That's 90 gallons water not a 90 gallon tank half full. Fill it if needed and make a "ATBA" above tank basking area ! Female's 12" needing a larger setup. A glass tank for an adult alone can run several hundred dollars , myself on a retied man's budget so I use stock tanks 1/4th the cost and last forever. I use the saved money for a good adequate filter. Be creative and one can make the outside of it look great. Also the foot print is much wider than any glass tank making turtle things easier to add.
Small water volumes are almost impossible for beginners to achieve a cycled tank ( due to only reading a basic care sheet ) , the large water volume's can hold a cycle easier which is your best friend on a cleaner tank so a proper sized filter with media for a turtle can do it's job. That's only one reason for buying an adequate filter/tank size , more reasons that can help care easier too. This will make maintenance much easier ! I know my setup has clean / healthy water and is matched for my turtle size . This is achieved with weekly water changes ( no way out of water changes) and with my setup I only have to clean filter once every 4 months , have gone 6 months and all still good. Can go into that for those who have an interest.
Most think changing larger water volumes will clear up a tank but that "Kills" all your good bacteria needed for a cycle. Never do 50% or larger water changes unless a health problem. One must find correct % for there tank being all setups are just a little different. 10-20% changes are much better , not killing off you good bacteria alone with proper water volume and filter.
Being an old timer I do not use "any" chemicals for my water but I use carbon to remove any toxins. Not in filter for that have a different method for that. Only things in filter are media tha can last 6 months or longer ! Most long time turtle keepers try to keep chemicals out our tanks so we have full control ! Captive turtles well treated can live 50 year's. And you being there only care giver / do it correct so the turtle can live those years happy and healthy. Many say pet turtle's only last the first year or two , this is due to the care giver and inadequate habitat's ! From "not" doing one's homework ! Be a good care giving and read all requirements needed for your species and have a new living pet/friend/child for a long time. They are great and have great personality's !
) but I've been struggling on finding a good filter. I've been through a couple already and the problem I seem to be having it they're just not strong enough. My turtle is pretty big so I had to get a pretty big tank (the one I have now is about 75-100 gallons) but all the filters at generic stores like Petsmart are for the little 10 gallon tanks. So I was wondering if you guys know of or have any really good filters for big tanks and/or know where I can look for one? Thank you so much 
