Its precision and compact design provides accurate readings that aquarists of any level can understand. Accuracy to 0.001 specific gravity units. Recommended specific gravity for most marine aquariums is between 1.021 and 1.023. Recommended specific gravity for most reef aquariums is between 1.024 and 1.026. Salt deposits that accumulate on pointer will result in incorrect readings. If salt crystallizes inside unit, soak in lukewarm fresh water or vinegar for 30 minutes, rinse with fresh water and let air dry.