First off, not disregarding ...

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First off, not disregarding previous comments/suggestions, you must identify the filaments. You cannot address the problem if you do not know the root cause. There are services available to assist in the identification, as it can sometimes be a tricky endeavor if you do not have experience in filament identification. I do not know where you are located, but some US based services are: https://teamaquafix.com/product-category/lab-services/; https://teamaquafix.com/common-wastewater-filaments/

https://mco-us.com/wastewater-microbiology/

Also, maybe a local university has this capability to assist you. I wish you success.