Monica Croston is the latest trainer in Victoria to have a horse return a cobalt reading above the allowed level.

Racing Victoria stewards have confirmed the Croston-trained Hezza Tidal Wave returned an illegal level of cobalt in a urine sample taken before finishing 10th in a 2400m race at Sandown on June 29.

Racing Analytical Services Limited detected cobalt at a mass concentration of 219 micrograms per litre in urine, while The Racing Chemistry Laboratory detected a reading of 240 in the reserve portion of the sample.

The threshold is 200mcg/L.

Earlier this month, Racing Australia announced the rule would be amended from September 1 with the cobalt threshold halved to 100mcg/L.