Producing Demineralized water from Ion-exchange resins

Hi every oneI hope you are all well and healthy.We planned to make Demin water out of municipal drinking water (Tap water), with a total hardness of 450 ppm, pH=7 by using the Ion-Exchange resin method. For this process, the Strong Acid Cation (SAC) resin,  PUROLITE C100 H, and   Strong base Anion  (SBA) resin PUROLITEA400 OH was used as Ion-Exchange media. The ion-Exchange was filed in an FRP Tank. (25 lit Cation and 50 lit Anoin resin). The desired ammount  of water was 300 liters in 8 hrs (M`=0.0375 M3/hr)First, the inlet water runs through PP and activated carbon cartridges and enters to Cation stage first, and then goes to the Anion, and after all, 2 mix bed cartridges with around 2.5 Lit of PUROLITE MB-400 resin.The TDS of outcoming water is around 40 ppm but the problem was that the pH of water is 9 to 10 !!!Then we added a Degasser tank after the cation stage,(a high 500 lit vertical tank with permanent air stream inside it, injected by a big bubble diffuser) the result was almost the same. I was thinking if we use (CATION > ANION >CATION > ANION > MIX BED) system, without degasser. But I don`t have any sense that what would be the result.Please help me how can I fix the pH.Thanks a million. A.Reyhan