Incubating problems

[addicted2chics]

I am new to chickens and even newer to hatching eggs. I built my own incubator from a large marine cooler. I built an egg turner that will hold around 75 LF eggs and even more smaller eggs. The temp in the incubator varies about 4 degrees. From 99 to 103 and the humidity i keep between 35 and 45 then raise humidity at lock down to 60 - 65. The first hatch was in Aug with about 97%. The next was Sept with about 99%. Oct was aboit 55% and has gone down hill from there. This last hatch was set to hatch Christmas day. Today I cleaned out all 20 eggs with hatch rate of 0. Am I doing something wrong, is 4 dehree temp flux too much or is it that time of the year?

 

[ChickenAndMore]

I think it is probably just the time of year, because my hatches always go down this time of year too.