Greetings,(posted 8544 days ago)I too agree with the water being the source of your problem. As a JOBO user (read continuous agitation) I can disprove the larger grain theory caused by increased agitation. The effect of constant agitation on grain size may be measurable from a scientific standpoint, but not aparent from a practical one.
I would not recommend the carbon activated filters. First, their level of effectiveness is not constant over their life. They can be highly effective for the first few gallons, but will change dramatically there after. Secondly, the carbon may not filter what's in the water, or may interact with the chemistry. I would stick with distilled water for the developer.
Regards,