ph and Alk low???

I had been battling a small gha since March and was starting to get ahead of it but ran out of Rowaphos 2 weeks ago and had to go with Phosban. I had been testing every week and all my parameters were always in line. Last week I noticed my toadstool was limping, my sps had no polyp extension and my acans weren't opening fully but my frogspawn, candycane and hammer etc were doing fine. I tested my water on Sunday here is where everything is at;

Sg 1.025
Ca 420
Amm 0
Nitrite 0
Nitrate 5
Phos 0.25
PH 7.5 tested twice
Alk 6-7 tested twice

The only thing that has changed recently is the change to Phosban from Rowaphos, replaced my GAC and cleaned my skimmer. I do weekly water changes (10%) using IO Reef Crystals with RO/DI. Is there anything I can do to get my PH and Alk up? TIA

 

Can I just add some baking or washing soda to bring up the values and if so how much.

 

bump for help please

 

I had that problem before and someone told me to run an airline from my skimmer to my window and it worked for me. Within a couple hours my ph was up to 8.1 I would try that.