7 aquifer layers? Wow
I can't deal with one XD
Yea the first time I tried to punch through an aquifer I had a LOT of water !FUN! subsequent attempts also failed (but without !FUN!)
One thing that really helps is taking advantage of the fact that aquifer tiles also absorb unlimited amounts of water, this is the underlying principal to what makes the twin slit method work.
So, if you think of what happens when you remove a single tile of an aquifer layer, you get a 7/7 pool of water where you removed that tile... The question is what happens if you remove the next tile down? Do you get two levels of 7/7 water in the shaft? Actually, you get a single 7/7 pool at the bottom of the shaft. The reason the upper level doesn't fill with water also is that the water is flowing down the sides of the walls, down to the lower level and being absorbed by the lower level of the aquifer. The only challenge is actually being able to dig out that second (lower) tile which is usually below 7/7 water above. To do that, temporarily pump out the first 7/7 pool so you can dig out the lower tile.
(Side view)
===== <-normal aquifer
==x== <- aquifer with up/down stairs dug into the first level (stairs will be filled with 7/7 water)
=====
PP <- place screw pump next to up/down stairs (I've also created a second hole in the aquifer to dump the water from the first hole)
x==x==
=====
(Not to over-complicate things but you need to channel out the stairs in order for the pump to remove water from that tile, just something to keep in mind)
x==x==
===x== <--- Now dig up/down stairs into second layer and remove screw pump after
Now, construct new stairs and the upper level stairs will have only 1/7 water flowing down the stairs to the level below where it is being absorbed by the lower aquafier tiles which will allow you to dig out the walls around the upper-level stairs and place stone to stop the water flow. Do this one tile at a time however.
This method should get you through! just be careful when you reach the last layer of aquifer so that you still have somewhere to dump your water. You can check if there's aquafier below before digging into it... When your miners dig up/down stairs above, the tile below will be damp if its an aquifer and there's no water above it. There's one or two ticks after the block above is removed before water pours in and makes the stone below damp where you can tell if its an aquifer or not but you need to proceed one tick at a time or you'll miss it.
Hopefully this is helpful and not TOTAL gibberish but feel free to ask for questions or clarifications or simply avoid the aquifers as you've been doing! Just trying to be helpful : )