Most macroalgaes prefer to consume ammonia over nitrate (but they aren't very picky, they take what they can get). This is why we don't recommend adding macroalgae to tanks while they are cycling. FYI, most macroalgaes will actually convert nitrate to ammonia within their cells (through the utilization of nitrate reductase).
With regards to the ammonia spikes, a good macroalgae will actually do surge nutrient uptake where it soaks up all of the nutrients it can find until its reserves are full. This is a great nutrient uptake strategy for ammonia spikes, however, you will likely need a decent bit of macroalgae. If you do a hang on the back fuge stuffed with sea lettuce, that should solve most of your issues.
You could also do something like marinepure for the high surface area, but since the ammonia spikes likely come in waves, the bacteria may not be able to maintain their population at the levels you would like (i.e. residual ammonia).