The men were in the final day of a four-month training programme run by Auckland company Helix Training. They were among five students supervised by an instructor and two assistants for the dive on July 15.
Constable Geoffrey Bray, of the national dive squad, told the inquest the dead men were carrying too much weight.
He said the depth of the lake, on Auckland's North Shore, was not checked before the dive and the student-teacher ratio could have been reduced.
He said all divers should have been carrying a torch, knife and watch. When Mr North's body was recovered it was still entangled in the descent rope - a plight made worse by his lack of a knife or torch.
Despite their training, Mr Bray said he was most concerned by the men's inexperience.
They had dived to 18m often, but 39m was the limit of their abilities.
"We're talking a dark place, we're talking a black place and a cold place. These men weren't experienced for this kind of thing"
Mr Bray said the instructor, Teauriki 'Nick' Tuaana, should have enforced multiple breaks during the dive. One was planned for a depth of 30m but did not happen.
However the parents of the dead men did not want to blame anyone for their deaths.
Mr North's stepfather Colin Amery told the court what he and his wife wanted most from the hearing was the truth.
And Mr Stoneham's father Cliff Stoneham said he didn't want Mr Tuaana to blame himself.
"I hear Nick has given his job away because of what's happened. I hope he can learn some valuable lessons and perhaps go back to doing what he loves because I don't blame him."
A family friend speaking on behalf of Mr Stoneham's sister Sheree said she wanted the coroner to make robust recommendations to prevent similar deaths.
"She also wants to strongly maintain the dignity of her brother who would not have wanted to lose his life because he had two daughters and a wife who he lived for. Sheree can accept that the tragedy has happened but will not accept that all the blame is on him."
Helix Training director Haydon Allan told the inquest yesterday that an investigation resulted in several changes to company policy but none would have prevented the deaths.
He considered the men who led the dive party to be experienced and had no concerns about the abilities of anyone taking part.
Coroner Matenga reserved his findings.