The four numbers that force a drain
Cyanuric acid. Once stabilizer climbs high enough that chlorine can no longer sanitize at a reasonable level, no amount of chlorine fixes it. Dilution is the only removal method that reliably works.
Calcium hardness. When hardness is high enough that you cannot hold a safe LSI without letting pH sit somewhere unhealthy, you are choosing between scale and etching. Dilution ends the choice.
Salt and total dissolved solids. Years of chemical addition leave residue behind. Very high TDS shows up as dull, flat-looking water that resists balancing.
Structural or surface work. Replaster, tile, and some plumbing repairs simply need an empty pool.
What does not require a drain
Green water. Algae is a chlorine and filtration problem. A green-to-clean recovery is usually cheaper and faster than a drain, unless CYA is also too high to let chlorine work.
Cloudy water. Almost always filtration, a chemistry imbalance, or a phosphate and organic load — not a reason to empty a pool.
Stains. Metal and organic stains are treated chemically. Draining alone does not remove them and can make some of them worse by exposing them to air.
Draining a pool in Central Texas is not risk-free
Our soil moves. Expansive clay and a high water table after heavy rain can push on an empty shell, and a fiberglass or vinyl pool can be damaged quickly. Even gunite pools can pop or crack under the right groundwater conditions.
Heat is the other hazard. An empty plaster surface baking in direct August sun can craze and check. There is a reason experienced techs prefer to drain in shoulder seasons and never leave a pool empty overnight without a reason.
A partial drain and refill often achieves the dilution you need with a fraction of the risk. If a company only ever quotes a full drain, ask why.
Practical sequencing
Check with your city before draining. Discharge rules, drought stages, and refill restrictions differ across Leander, Cedar Park, Round Rock, Georgetown, Liberty Hill, and Hutto, and they change with lake levels.
Test the fill water before the hose goes in so you know what chemistry you are starting from.
Plan the balance immediately after refill. Fresh Central Texas tap water is not balanced water — a new fill needs calcium, alkalinity, stabilizer, and chlorine set deliberately, or you spend the next month chasing it.
