Hi Stephen and welcome,
You were not wrong to increase the depth to try to anchor your bait down, you were just using the wrong bait for the particular water you were fishing, you obviously have some experience, just keep asking the questions you need answered and you will find we are a friendly site and you will get most of the info you need, ( for example ) Soak your spool of line in a diluted washing up solution, this will help it cut the surface of the water- overcast and sink the line by dipping the rod tip under the water and quickly give the handle a couple of turns keep the tip just under the surface and this will help stop any drag. occasionally put a bit of washing up liquid on a small piece of sponge, cast down the canal / lake and wind the line back through the sponge ( dont forget the most important bit from the float along the length of the rod )
Best of luck