There is an additional problem with the method used to make metaborate as gien on the web. Borax IS soluble in water. If you add sodium hydroxide until the slurry of borax just dissolves this does not take into account the borax that was already in solution when you started. The method is very imprecise. That is why I advocated weighing things out in this case. For Kalogen and Rodinal the solid IS NOT soluble in water so this kind of error does not occur.