Last summer I was told by Leslies my pool had an unusually high salt level due to my using liquid chlorine. Is this true?
I've used powder shock ever since but am having an algae problem again and am tempted to go back to liquid.
Chlorinating liquid and bleach (and also Lithium Hypochlorite powder) will add salt to the pool about twice as fast as Trichlor or Dichlor. But that doesn't matter very much unless the salt levels get very high. You shouldn't worry about it. Saltwater chlorine generator (SWG) pools have a salt level of around 3000 ppm, for example.
If you use powder for shocking, which is probably Dichor, then that increases the Cyanuric Acid (CYA) level and makes chlorine less effective. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. You either need to maintain a higher Free Chlorine (FC) level to compensate, or use a supplemental algaecide (at extra cost), or not use products that increase the CYA level, or dilute your water through drain/refill or more frequent backwashing (if applicable) to keep the CYA lower.
You should invest in your own good test kit -- either the Taylor K-2006 or the TF100 at tftestkits.com.
Pool stores that don't sell bleach tend to say bad things about it so you will buy products that they do sell. All forms of chlorine effectively contain salt, since disinfecting chlorine breaks down into salt as it gets used up. Bleach does contain more salt, but not enough more that it will make a significant difference. As long as your salt level is below 5000 you are fine. I can't imagine the salt level getting above 2000 from using bleach for years and 1000 is much more common.