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Hi @cryprofrench, that's a really good question. All Steempower gained by the witness will be payed with liquid Steem from my account in a 1:1 ratio of course. On the 1st of each month the total amount of Steem is send to steemhq.witness and payout for each participant is proceeded from there.

So this problem is taken care of as I act as somekind of liquidity provider for payouts.

Thank you for this answer.

I was currently making some calculations on how to do this kind of witness rewards but I was quit confuse on how convert SP to Steem and I end up with only one solution : You need a tone of Steem even before starting the Witness.

As you have a old account it seems that everything will go well.
Is it possible to contact you in private somewhere ?