After being cooked, the seaweed gel in Eucheuma cottonii dissolves in water. To remove sand, shells, and insoluble residues from this heated gel, a hot gel filter press is required for coarse filtration. However, due to the high viscosity of the gel and the ease with which cellulose and hemicellulose clog the filter cloth pores, directly filtering this viscous gel is very difficult. 

The common practice is to add perlite as a filter aid during the cooking process. Perlite is obtained by heating small-grain mineral sand to expand it, followed by grinding and purification to achieve a specific particle size powder. Compared to other filter aids like diatomaceous earth, perlite has advantages such as fewer harmful components, lighter density, and faster filtration speed. Therefore, it is widely used in the production of carrageenan, agar, and pectin. The methods of using perlite as a filter aid include using it alone or mixing it with activated white clay, which can significantly improve product clarity and filtration speed, and facilitate the cleaning of filter cloth. Additionally, the filter cakes produced using perlite as a hydrocolloid filter aid can be used as plant growth media.