Seachem Acid Regulator 250g

"Acid Regulator™ adjusts pH to the acidic range (4.5–5.5) and softens
water by precipitating calcium and magnesium. Acid Regulator™
supports the establishment of the optimal environment for all acid
acclimated species (e.g. neons and other tetras, etc.). For further
freshwater environment enhancement, use Fresh Trace™ to restore
the proper level of trace elements and feed NutriDiet® Tropical
Flakes for thriving, healthy freshwater community fish.
Contains phosphate buffers and conditioning agents.
Safe for all freshwater fish acclimated to acid pH."