I'm not sure if H2O2 can really promote root growths. I quickly looked into it (in scientific lit.), but I didn't see it (note that I just spent only 20 min or so). H2O2 is an important molecule in plant physiology. It is involved in defense against pathogen, prevention of damage due to a byproduct of photosynthesis, seed germination etc. Also, it appears to be involved in the response to stress (UV, drought etc), and there are some suggestion that it may act as a messenger (hormone). They are more related to STOP signals, so I would be cautious.
I'm not sure if full text is available, but this paper has a good review:
Quan, L.J., Zhang, B., Shi, W.W. and Li, H.Y., 2008. Hydrogen peroxide in plants: a versatile molecule of the reactive oxygen species network. Journal of Integrative Plant Biology, 50(1), pp.2-18. (
link to abstract)
It doesn't have to be Kelpmax. Since you don't have the location data in your profile, I'm not sure where you are located, but there should be lots of other seaweed products (e.g. MaxiCrop) with auxins (hormones which is involved in branching of roots). Or synthetic auxins like NAA or IAB are available (DynaGro K-L-N, Superthrive etc). Vitamin B2 seems to be not effective for rooting, though.
But before going with the hormones, are other parts of culture OK (Light, Temp, RH etc)? If you are not using artificial light, the amount of light is decreasing at this time of the year.