Interesting. I’ve been having a some intermittent ‘curious’ readings from my trident for calcium as well. Was away on holiday last week and got an alert that calcium was low. It had been trending in the mid 400s, but all of a sudden I’m alerted that the levels are in the low 300s. Since there’s really no way for calcium in my tank to drop precipitously without attendant moves for alkalinity, I figured it was a measurement error so no panic necessary. Readings continued low for a couple of days until I see ‘test B fail’. Ah ha, reagent B must be low (a little disappointing since it’s only been running for 6 weeks, but ok). Except then, on the next round CA reads properly again (nominally 450) so apparently the reagent is not low - which I confirmed upon getting home last night. Maybe the feed tube ingested a bubble - but surely that would affect the other two tests also. Likewise if it ingested a detritus particle. I like the trident a lot, and WOULD recommend it if asked; but this is exactly why I do not use it to trigger any actions ..... only alerts.
