With tanks that size stacked up, I would be building the stand out of steel.
Looking at the weight factor each tank set up would weigh about 500kg.
Top tank would have it's base at about 1800mm high, long way up, would need to strap it to the wall for stability.
I think that the concept would work.
But I would look at only doing it 1/2 to 3/4 across width of tank so you can feed and do maintenance without having to remove it.
Hope you mean Methylene blue and not blue meths.
What filtration is on the tank ?.
Methylene blue will have some affect on the bacteria in your filter.
Make sure water is well aerated and reduce flow to filter.
I would do a large water change (50-60%) after three days and add carbon to filter to remove the rest of the methylene blue and do small (15-20%) water changes daily for a week till bacteria in filter grow again.