Garmin fishfinders,need info anyhelp

I've been looking at some of the garmin ff,now I'm not sure but from what I'm reading are they water specific,meaning is there a unit that's for saltwater and one for fresh.or is it just the transducer.I've been trying to research it but no luck on it

The FF-ers I have gotten have worked in both aquatic conditions...even in a pool! The only difference in between salt and freshwater are the max depth readings. The salt water might not allow it to read as deep as the max depth states. No biggie unless you're going in super deep water. Good luck.

The fish finder should be able to operate in both fresh and salt water. On my Humminbird, one of the setting is between fresh and salt water. This is to better calibrate the water depth measurement since salt water is more dense than fresh water, so there is a slight difference in the time it takes the sound wave to travel to the bottom and back. But the difference is negligible when compared to the swell height in the water depth I fish in (< 120') so I just leave it on salt water.

I have an echo 150. I mainly use it in the salt, and only once in fresh -works as expected. Structure, bait depth and temp. Also I am shooting through hull using the foam donut with water method.
I do believe the Max depth reading change from 1500 feet for freshwater, and 600 for the salty stuff. Not really worried about as my deepest expected depth is less than 200!

you should buy a transducer which will work best for you primary depth of fishing; a transducer which works in a 100' of salt water will work in a 150' of fresh water... with a 20 degree cone which is standard on most transducers.

the more power the tranducer has, the deeper you can see; but it will use more battery power to do it....

From my experience, most of it has to do mostly with the transducer.  Dual beam transducers - 83/200 khz for freshwater and 50/200 khz for saltwater.  Like the others said, it has to do with the transmission of the signal through the water.  The bottom number is what you should be concerned with.  50khz usually has a wider cone and travels better in deeper dense (salt) water.  Where the 83khz usually has a narrower cone and has a little more detail in shallow water.  If you are going to fish both salt and fresh water, I would suggest getting one that does 50/200 khz.

Thanks for the help everyone,I've got a old Lowrance x96 portable unit.that I bought from cabelas,I use it when I rent boats,so I use it maybe 3 times a year.and I had it for about 5 years I think.I saw the garmin 550c and I'm trying to get it for 350.the one on my yak is a Lowrance elite 5x which cost me almost 400.so as I was doing the research online, youtube,etc.they keep mentioning that it's designed for use in freshwater and that it's extremely clear so I got a little concern.so after all the searching I knew that there is always alot of knowledge here.so I'll be deciding on the 550 or th eagle cuda350c it's on sale for 129.99 at cabelas.