I wouldn't dip the fish. The stress will most likely be worse than the ich, unless it is really bad. If there are a lot of open wounds/ich do not use formalin. That's like disinfecting a large wound with bleach/peroxide. Does more damage than good.
If I would dip I would do a FW dip. This means cathing the fish in a bag not a net. previously having a few gallons of equal temp buffered FW floating in the tank for equal temp and so the buffer has reacted. Then catch the fish with another bag or tupperware container. Then place it in a bucket with some of the tank water frim the bag. Then slowly over a period of time lower the salinity by adding FW from the floating bag. Lower the salinity no lower than 1.008-7. Lower won't really help much for ich but can severely stress out the fish. Then leave the fish at 1.007-8 for 45 min to an hour. Put a drop of amquel in the bucket for ammonia. Then after the treatment is done scoop the fish out with a container and transfer it. Meanwhile it is a good idea to lower the SG in the tank to 1.018-6. This will help with your ich and improve waterquality. But won't kill the ich and hopefully any other inverts and life on the rock. I suggest moving the LR and doing small waterchanges with dechlorinated, buffered FW, with excess amquell for the ammonia. Lower the SG to 1.010. You can easily prepare cycle the existing filters to handle the new bioload in that time. If money is an issue, I'd simply get some brilliant filtersponges for powerheads, if not get a large fludized bed filter. Maybe a large 600 or 900 Rainbow lifeguard, whicch will be a good investment for the large new puffertank. try finding a seperate container to quarantine the angelfish, since they will react much worse to these bbad waterconditions.