bro... the pH shouldn't... there are kalk reactors out there which have powerheads stiring kalk w/o any problems... but if u are talking abt soaking the powerhead in the kalk solution then I think it's a different matter, coz the wire might get corroded..
and the pH is high.. it's 12 leh... although not as bad as acid it'll still corrode things quite easily..
Also, not the best idea to have the kalk in the reservoir because there will be air in the reservoir.. u want the kalk solution to not touch air as much as possible...
lastly... i also have an DIY auto-top which delivers kalk solution.. but the water reservoir only holds water, all the kalk is stirred in the DIY kalk reactor..
so it's water reservoir --> kalk reactor --> tank