This is one of the main supplements that gets used in aquaponics. Seaweed extract. It contains potassium and trace elements that are safe for fish and can help get a new system up to speed on the things that are not going to be provided by simply fishlessly cycling a system with pure ammonia.
The seaweed extract doesn’t provide enough nitrogen to risk overloading the bio-filter which is why it is generally quite fish safe.
It doesn’t take a whole lot, a cap full or splash per growbed (depending on the size of grow bed) is about all that is needed per dose and dosing might be once a week or once a month and less often once a system is well established unless plants show signs of needing more potassium or trace elements.
One Quart or 32 oz size $12.35