I recommend putting a captchas limit because if it continues so the Threshold will continue to rise to infinity and it will be impossible to collect.
It's only possible if claimers won't sleep at all. As the claimers log off one by one or as they reached the quota, the threshold also lowers paving the way for others to make the threshold too. Upon reaching the quota, you're claim will be zeroed in and so the cycle goes on. It's only fair I guess.