Another thing I've noticed about the Oxi-Clean wash is that it tends to leave a whitish residue particularly on the areas of rough grain and around knots, which becomes more noticeable the longer the wood is left to dry. I wondered if it might be calcium carbonate deposit or maybe inert filler from the powder, but it doesn't seem to come off after more rinsing. I can only assume that is actually residual dead/dying wood fibers that have become 'bleached'. The Biovert product definitely gives a much cleaner result, but at the expense of some erosion of the underlying wood.
I contacted Biovert to ask if they could provide more information on their product. Whilst they would not disclose the actual formula, they confirmed that it did contain only sodium percarbonate and sodium carbonate and that the % of the latter was 'much less'. In Oxi-Clean, it is the reverse - 55-75% sodium carbonate and 30-50% sodium percarbonate.
Sodium carbonate does play an important role in these oxy-bleach products by raising the alkalinity so that the percarbonate is activated, but I came across this interesting link which suggests that the sodium percarbonate content needs to be at least 75% in order to be effective as a deck wash.
The poster (a developer of oxy-bleach products) also indicated that addition of Sodium Metasilicate (as a TSP substitute) is beneficial, although not explaining why.
I reckon the BioVert powder must contain around 75% percarbonate. I would like to try adding sodium metasilicate to the solution to see if it can reduce the amount of etching/erosion.
Does anyone in Canada (Quebec in particular) know where I might be able to find (relatively) pure sodium metasilicate? I've tried the usual hardware outlets - Home Depot, Reno Depot, Rona, Canadian Tire, Ace. The only 'TSP-substitute' with metasilicate I've found contains other chemicals (ethanolamine, sulphonic compounds etc) as well.