All new or replace as needed?

Stored indoors or at least out of the sun, heat, and rain? If so, you're probably good to use them all up. If stored in a situation where a cat might not fare so well, then they might have prematurely met their demise. No harm in testing with them and seeing if the results make sense. TFT sells a refills kit that doesn't make you pay for the box/hardware so you can save a little there if/when you refill some/all be sure to see if a whole set is cheaper than just the ones you need. Since you have vinyl - as long as your fill water isn't calcium ridiculous you could even ask them to skip the calcium and give you a little extra of something you use. Can't promise anything, not affiliated with tftkits.
 
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