Dosing Kalkwasser in ATO

[GHD1959]

I have a bio cube 14 and I just started dosing kalkwasser last night. I used the lowest dose of a half a teaspoon per gallon in my ATO and I'm wondering it's only a two and a half gallon reservoir so I put in a teaspoon and a quarter but my hose runs into chamber three where the return pump is so I'm wondering if that will actually work or will too much of the solution actually just sit in the chamber before it's picked up by the return pump to send back into the tank

 

[GHD1959]

Here's a picture of chamber 3.