Best way to solve this...
New members join and have to donate X amount in the first two weeks...
If they do... they stay on as members, if not we get shot of them...
Members need to donate X amount every two weeks...
If they do... they are promoted to elder, if not we get shot of them...
You keep elder status by donating X amount every two weeks...
Failure to do so you get demoted to member, requiring you to donate to get promoted...
This basically equates to a system where any member with <X troop donations getting kicked... any elder with <X troop donations getting demoted, and on the flip side... >X means promotion to elder etc...
You can make it harder so 200 to stay at member but if you stay at elder you have to reach 500...
It'll lead to high donators (those who are on more) staying as elders, who can then help moderate the clan.
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To make it easier to understand...
On the sunday at the end of the two week period:
New members need to have donated 100 troops to stay.
Members donating less than 200 are kicked.
Members donating more than 200 are promoted to elder.
Elders donating less than 500 are demoted to member.
Elders donating more than 500 remain as elder.
So for me... I am elder and have only done 300 this 2 week period... I will be demoted to member and thus need to donate more than 200 to become elder. Failing this will result in a kick.