Cov khoom siv thiab hardness yog qhov tseem ceeb heev rau lub neej ua haujlwm rau cov hniav, raws li ntau tshaj 35 xyoo kev paub, Renda Blades tuaj yeem muab tswv yim rau koj thiab pom zoo rau koj cov khoom tsim nyog thiab hardness raws li daim ntawv thov ntawm cov hniav nrog cov nqi sib tw.
Txhawm rau muab cov lus hais sai thiab raug, nws yog qhov zoo dua uas koj tuaj yeem muab peb qhov ntau, kos duab, txiav daim ntawv thov thiab lwm yam.