I've found that I occasionally get a much smaller hash rate than my actual one displaying on the website. For example, multiminer is reporting 230 - 250 khs, but hashcows has thought I've been 50 - 100 for the last two days.
I really want to keep mining here, so can anyone give me any ideas on why this might be? Thanks!
kh/s on your side does not matter at all when it comes to being paid. All pools pay you for how many shares you actually submit back to them, not the rate you are trying to figure them out. On pools when they quote your kh/s it really is your shares submitted divided by time. In cgminer this is the display variable U, which is in two places- one for each card and then totaled at the top combining all. Your share submission also varies a lot with luck, and even temperature. On one rig I have two 5850s each mining at 350kh/s. One is submitting at 1.67 and the other at just 1.6. You can slightly tweek how many shares your cards submit by keeping them as cool as possible, using proper thread concurrency, or even lowering gpu ram voltage (which is different from card voltage, which you should run as low as possible as well for cooling and electric savings).