Adding a continuous effect that grants +0/+0 to a creature has absolutely no impact on any counters on that creature. Counters are physical game objects placed on permanents (CR 122.1), and they remain on the creature until a spell, ability, or game rule explicitly removes them.
A continuous effect that modifies power and toughness (CR 613.3) simply adjusts the calculated values of those characteristics — it does not interact with the counters themselves. The -1/-1 counters are still tracked separately and continue to apply their own layer-7c modification to the creature's power and toughness (CR 613.4c).
To remove -1/-1 counters, you need an effect that specifically says 'remove a -1/-1 counter' (or similar wording), such as Archipelagore's ability or Hapatra's Mark. No amount of +0/+0 buffs will accomplish this.
Concrete example: You have a 2/2 creature with two -1/-1 counters on it, making it effectively a 0/0 (about to die). If an effect grants it +0/+0, the creature is still 0/0 — the counters are untouched, and the creature will still be put into the graveyard as a state-based action (CR 704.5f).
In short, power/toughness modifications and counters operate in parallel layers of the same calculation; a +0/+0 effect adds nothing and changes nothing about the counters themselves.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.