My turtle is getting to big for his tank, but they don't seam to make them bigger

I need something that is WIDER, not taller, not longer. it's frustrating not seeing anything out there

He also is going to need a more active filter

I've been having to change it alot more often recently, and his water gets very VERY icky very quickly.. cause he's big now
*Sigh* anyone else ever have a similar problem with your animal?