Customer's HOG3 or 3x or 3xx in saltwater, with very light colored growth. Just like vegetables, darker growth means more iron is in the growth, and other nutrients too; so you can add iron to the water (with supplement drops) or feed more seaweed like nori or algae pellets to the fish, which will also eventually get more iron into the water, and make darker growth.

Also note that the filter does not have to be completely underwater; the top part can be above the waterline. This is also the way to block salt spray.

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