Just get an RO/DI as soon as you can. Algae is a natural part of the cycle, it is actually helping you out by eating up much of the nutrients in the tank. It looks horrible but its not entirely a bad thing, although the sooner you get proper water in the tank the sooner you will be able to get rid of it. It may take sometime to get it all out though, so be patient. The initial cycle may take a month or so but truly the tank doesnt really complete the cycle for a year or more before it becomes fully established and a thriving ecosystem can be maintained. Alot of factors can go into determining how long it takes though, everything from where your live rock came from, how long it has been in water, if it was ever dry at any point, where your sand came from and even your experience level are all factors that play into how long it takes to get a well established tank.
Once the initial cycle completes and numbers are all in line I would just start with a clean up crew of sorts, some assorted snails and crabs. Then wait awhile more before adding anything else. In the mean time just pull out as much of the algae that is waving in the current as you can. I would also increase your flow rate by quite a bit to. 75g tank should have a bit more then double what you are currently doing.