What to buy, how to set up, and what to stock in brackish aquariums. Equipment lists, sizing rules, stocking ideas, and the most common mistakes.
Brackish tanks (specific gravity 1.005-1.015) host species that cannot thrive in pure fresh OR salt water - mollies, monos, scats, archerfish, mudskippers, figure-8 puffers. Brackish setups are uncommon because the livestock pool is narrower and most LFS do not stock brackish-only species, but the look is striking and the stocking options surprisingly diverse once you commit to the salinity range.
Core stack: tank (40+ gallons recommended for adult mollies/monos); marine salt mix (use real reef-grade salt, not aquarium salt); refractometer to maintain SG 1.005-1.015; canister or sump filtration sized 5x display; heater; sand or fine gravel substrate; mangroves or salt-tolerant plants; water-change buckets dedicated to brackish.
Light: standard freshwater LED is fine; intensity matters more than color when stocking is mostly fish. Filter: 5x volume canister or sump; brackish water tolerates higher bioload than fresh due to oxygen-carrying capacity differences but the trade-off is harder ammonia spikes if filter is undersized.
Brackish-only candidates: mollies, monos, scats, archerfish, figure-8 puffers, bumblebee gobies, mudskippers, knight gobies. Most "brackish-tolerant" freshwater fish stress at 1.005+ SG and shorten their lifespans, even if they survive.
Most-common mistake: using aquarium salt instead of marine salt. Aquarium salt does not contain trace elements brackish species need; use a reef-grade marine salt mixed to your target SG.
$400-1,200 for a 40-75 gallon brackish setup. Salt + mixing equipment is similar to saltwater but skimming is optional, which lowers the equipment cost.
Yes - this category has solid beginner-friendly options when you size appropriately and stock conservatively.
A timer or controller for lights and equipment - manual switching introduces variability that biology doesn't like.
4-6 weeks for freshwater systems with bottled bacteria + an ammonia source. Plants help by absorbing ammonia directly.
Most freshwater tank types convert easily between each other - swap substrate, hardscape, and stocking. Brackish to fresh requires careful salinity reduction over 4-6 weeks.