A key member of the 'Aquanita eight' has admitted administering illegal race day treatments for trainer Robert Smerdon and other members of a "circle of trust", but denies doping Melbourne Cup horses.

Float driver Greg Nelligan initially maintained only he and Smerdon were involved in the cheating conspiracy, before implicating the other people banned for their roles in Australia's biggest racing scandal.

Nelligan said he and Smerdon had an agreement that a "top-up" meant administering sodium bicarbonate and Tripart paste to horses on race days.

"Between Robert and myself it later became a signal to do a race day treatment," he told the Victorian Civil and Administrative Tribunal on Monday.

After being subpoenaed to give evidence in the appeals of four trainers, Nelligan admitted the top-ups practice occurred for "some years" before he was caught in October 2017.

The 60-year-old said he was not paid to give the top-ups and did it only because "I was asked".

Nelligan, who was banned for life over 123 race day treatments over seven years, said the majority of times he only pretended to give horses top-ups and did not actually do it.

"Quite often they'd say top up this horse. I'd agree but I wouldn't do it," he said.

"I'd just pretend I'd done it.

"I was frightened of being caught every time."

During his early evidence implicating Smerdon who was also banned for life, Nelligan maintained he only actually administered the top-ups a maximum of 20 times.

Nelligan was then asked about some of the 1000 texts found on his phone after he was caught inserting a syringe into the Smerdon-trained Lovani's mouth on Turnbull Stakes day in 2017.

VCAT heard Queensland trainer Liam Birchley texted Nelligan asking for a top-up on the eve of Melbourne Cup day in 2015.

Nelligan responded that Smerdon had ordered five and he had "two Cup horses as well".

He texted: "Robert had me do one for the guy with the Cup horses a few years ago so it's not out of the circle of trust but I still don't tell him."

Nelligan on Monday said he had no recollection of the administering top-ups for the unnamed guy with the Cup horses and no idea why he talked about giving them to two 2015 runners.

"I remember nothing about two Cup horses," he said.

"I never did a Cup horse."

Nelligan admitted there was a circle of trust who knew about the bicarb top-ups on race days, implicating the other members of the Aquanita eight including his wife Denise.

Eight people associated with thoroughbred management company Aquanita Racing were disqualified from racing.

Smerdon and trainers Stuart Webb (four years), Tony Vasil (three years) and Birchley (one year) have appealed.

Nelligan, who prefaced his responses to questions with a legal claim that his answers may tend to incriminate him, will continue his evidence on Tuesday.