I need detailed instructions for converting algae into algenic acid.

There are a number of protocols available that use ethanol instead of formaldehyde here's one.

https://www.sciencedirect.com/science/article/pii/S2772753X24002089#sec0013

This articles protocol is as follows:

1. Harvest algae, wash with tap water, soak in chlorinated water (25ppm) for 30min then dried at 45C.
2. Grind dried algae and store in airtight container.
3. 6g of dried sample wash soaked in 99% ethanol for 3h then dried again at 40C, repeat.
4. Pretreated algae then had 30% citric acid added til pH was 1.
5. Sample was then ultrasonicated (180W, 15min). Washed with distilled water.
6. 2% sodium carbonate added (w/v) pH10 with magnetic stirring for 90min at 80C
7. Filter, supernatant precipitated by addition of 2 volumes 100% EtOH, centrifuge and dry pellet at 40C for 15h.