Aquarium substrate choice depends on tank type + livestock + plant goals. Inert sand (community FW): CaribSea Super Naturals, Black Diamond Blasting Sand, pool filter sand. Pros: cheap, never needs replacement, looks natural. Cons: doesn't feed plants. Use for tetras, livebearers, cichlids, corydoras. Aquasoil (planted tank): Fluval Stratum, ADA Amazonia, UNS Controsoil, Tropica Aquarium Soil. Pre-loaded with macro + micronutrients. Pros: explosive plant growth, lowers pH/KH (good for South American). Cons: leaches ammonia for first 2-3 weeks (cycle hard), depletes after 1-2 years. Aragonite reef sand: CaribSea Special Grade, Fiji Pink, Reef Saver Bahamas Oolite. Pros: buffers pH/alk, great for reef. Cons: cloudy when first added. Bare bottom: SPS reef tanks, breeder grow-outs, hospital tanks. Pros: easy waste removal, max flow. Cons: stark visual. What to avoid: colored gravel (toxic dye risk on cheap brands), crushed coral in freshwater (raises pH/hardness unintentionally), painted gravel in shrimp tanks.
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