Yes they can stack ,if you want access to the lid i would put something between the tanks to lift top one up to give access to one below.Can you stack them? Farmer mate had 6 I think. They had man sized inspection hatches on top (& Co climbs into the 200L tank to clean - then I showed her a hidden power socket you can plug the wet/dry in which is easier )
That’s $60-70 that’s a whole heap of Ph Down. I guess one of those. Ooh but you got me thinking.
One of those (4x4 as it fits on a pallet) as the flower fert mixing tank. Fill the 200L off that and Ph down the 200L daily, big ticket items like the Bloom Explode just add in to the 200L with the base in the 1000L. Use the 100L for veg as they drink less then. Its going to be a choice between one of those and a 4x4 for cloning and breeding.
If it was me and I had kids around and other people I'd probably tack weld top to bottom to stop any accidents happening