If you use kitty litter get the ultra plain stuff, no
odor treated or pretty smelling.

I guess you also might be able to use untreated soil from
your garden, wet it down good with pond water and slooowly
lower it into the pond. I'm all about trying to stick as close
to Mother Nature's way of doing things as possible.

My frogs do fine in our lined pond. The amount of muck down
there depends on the year and how ambitious we are in the
spring when we clean, if we clean at all that year.

When I have lost frogs it has been because of a power outage
and massive snow which ices over the pond for an extended
period of time. I use an air pump to keep a hole open in the
ice.

k :-)