Based on your post my guess would be that your cya is higher than you think and therefore you are not using enough chlorine. If you are using trichlor continuously, then you are adding cya all the time. Since, normally, the only way cya gets lowered is through water replacement, your cya is probably always increasing. Over 100ppm is difficult to measure (and I've found that getting an accurate reading is difficult at best and lighting plays a role in the accuracy too.) So I suggest you stop using trichlor and begin chlorinating for cya over 100. Anyone else have other thoughts?