Not sure about using H2O2 for correcting diatoms/ugly in maturing tanks. Let the ugly stage happen, it'll all go away on it's own time and usually fairly soon. I was going to after diatoms were causing me some frustration and a reefer here talked me out of it. Just be patient and it'll go away on it's own without risk. I was and it did a week or so later. Very happy with waiting.
H202 is a fairly potent chemical and in a small tank could have some negative consequences unless used very carefully. It's a great solution for problems, just don't think maturing algae/diatoms blooms are a problem that needs that level of correction.