Hi Kaley, it sounds like your starter is just going through a lull in rising, which frequently happens around day 4 and can go on for several days. Since it took me so long to get back to you, it may well be that your patience and persistence have prevailed and your starter is now rising and doubling predictably. I hope this is the case, but if your starter is still not rising then you might want to consider the alternative feeding plan that I've suggested to many who have experienced a similar lull. This method was recommended to us by microbiologist and sourdough baker, Debra Wink, and is meant to increase the acidity of the starter, which helps pave the way for more yeast activity. Here's the plan:

1. Feed once a day.

2. Feed with whole wheat or whole rye flour. If you don't have these flours available, you can use AP flour. 

3. Feed with a ratio by weight of 2 parts starter : 1 part water : 1 part flour. For example, save 1/2 cup starter (4 ounces, 113g) and feed 1/4 cup (2 ounces, 57g) water + 1/2 cup (2 ounces, 57g) flour. 

Once your starter is rising predictably you can switch to feeding according to our regular sourdough starter recipe with the twice a day feedings and equal parts by weight of starter, water and AP flour. Don't be surprised if your starter lags a bit each time you switch up its feeding routine, as the organisms need time to adjust, but once the starter is rising predictably with this routine, then you should be good to go! 

I don't think using a copper measuring cup a few times would have caused any damage to your starter, but I wouldn't recommend storing your starter in reactive metal containers like copper or aluminum. 

I hope this helps! 

Barb

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