Maltodextrin can be added at kegging or bottling time if you determine the beer is thin. Maybe boil about 4 oz and add to beer. Not sure about amount. This way you can still brew and pick it up later. Or 1/2 lb plain oatmeal.
Try a restaurant supply store if you have one near you. They have smaller plastic food grade storage containers with sealed lids that will work after you add an airlock.
My 10 gallon Spike is perfect. That one is just one that slipped through. It happens. They are rectifying the issue, so now it becomes a non issue. I will order from them again.
I am no water chemistry expert, but I have asked some questions concerning gypsum additions in IPAs. Based on what I have been told, you may want to include more gypsum for a 13 gallon batch. Maybe post this question on the Water chemistry board.
Brewing a session IPA and trying to get my calcium closer to Brun Water, but cant seem to do it without adding too much chloride. Any suggestions or leave it alone? BTW, I am no water expert.