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.