Love your kind of questioning Steve!
This is very relevant when fishing big deep pits and resi's as what pops up in a jar doesn't necessarily pop up or rise in deeper water. Two main factors are at play namely;
a. buoyancy
b. water pressure
As you know, the deeper you go, the greater the pressure
The more buoyant a bait (or object) is, the more it will counteract/compensate for the pressure and rise... but nothing like as much as it would in shallow water.
Air will compress easily, especially injected into a thin worm skin, whereas the air entrapped in cork or a polyball should (in theory) be a bit more boyant? An air injected worm retrieved would still float normally however.
As an alternative to worms, or maybe there's some floating worm lure to try? would be good with one of those hooks that float... Bigger, more buoyant baits are the way to go as are the type of material used at greater depth and who knows whats down there, there could be hundreds of years worth of silt? A long hooklink would be called for if you were to avoid the lead dragging it down.
Coloured poly balls wrapped in paste would be how I would approach the problem, either that or just a white/bright poly ball and a fast dissolving pva bag of feed/chum on the lead clip. To cast out any great distance maybe pva string attached to a stone as well as using the lead to hold bottom? Compensating then for the weight needed just enough to hold bottom once the pva strings gone.
When feeding, PVA bags don't melt so quickly at greater depth where its (usually) colder (with the exception in winter where surface layers are frozen, but its still cold) so maybe consider alternatives to pva such as a cage feeder? but bearing in mind... if its a long way down it might empty on its travels before it reaches bottom? I'm sure there's an alternative you can come up with.
Google says; A cubic metre of pure water at the temperature of maximum density (3.98 °C or 39.16 °F) and standard atmospheric pressure (101.325 kPa) has a mass of 1000 kg, or one tonne.
How that relates to the kind of water and depth your fishing is not so easy to interpret, but all I know is that water is never pure, temperatures and densities vary at certain levels as do atmospheric pressures.... this much I do know... anything over 10ft and my ears pop!
One last thought, and BTW there is no such thing as over thinking if it improves the way we fish
... I imagine even a poly ball or cork ball at a depth of 30ft or more would act more like a wafter than a pop up?
Keep those questions and answers coming Steve and please don't be discouraged, its very thought provoking and some of us might learn a thing or two, we never stop learning! Good post mate.
NB. Tech please address server error I got when attempting to post earlier: Fatal error: Memcache is not installed in [path]/includes/class_datastore.php on line 186
