I have just calculated the capacitance of each tube, being the internal tube 1,27mm diameter X 500mm long Than the capacitance is

199cm2 = 0,0199 m2

Relative constant of water 81

Absolute constant = 707 pf /m2

1mm = 0,001 meter

So (Area m2 * absolute constant / distance in meters

So 0,0199 * 707 / 0,001 = 14.069 pf or +- 14 nf

If the gap is 1,5 mm the capacitance become

So 0,0199 * 707 / 0,0015 = 9,379 pf or +- 9,4 nf

You see?

If this is the capacitance than to ring at 5khz the inductor must be around 100 uh witch is quite reasonable for a high current inductor.