The size depends on your goals and available space. A good starting point is a 1000-liter (264-gallon) fish tank with a 2000-liter (528-gallon) sand biofilter. The key is maintaining the correct volume ratios (1:2 fish tank to biofilter).
This is covered in Section 5 (System Size) and Section 6 (System Ratio) in The Fundamentals of iAVs. Section 5 defines the standard modular unit, and Section 6 details the validated tank-to-biofilter ratios you need to maintain.
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