Deadly Residue/Algae?

O.K. I COMPLETELY emptied the water from the pond (Not a single drop
left, pond completely dried). I did not find any leak. With the pond
completely empty and dried, I walked around it and thoroughly examined
it. The pond was emptied of all pumps, all rocks, everything. I did
not feel any evidence of water under the pond liner, or any water
leaking into the liner from outside. I noticed that there was some
green algae-appearing material on about 50% of the pond walls, and
some whiteish residue on about 25% of the pond wall surface. I got
into the pond and scrubbed the walls completely. The pond was rinsed
and the procedure was repeated twice (no soap just water and a brush).
The pond was completely clean, no residue, no algae. You would need
a magnifying glass to find any speck of anything on the liner. The
pond was refilled, and treated with dechlorinator and a chloramine
detoxifyer (Beckett product). A goldfish was acclimated and released.
So far it looks good. Will update. Now I can truely say, I do not
believe there is anything left to explain if the fish dies.