Thanks OC. I
am doing what I know to do, plus the
great advice I've been getting from this forum. Mostly, in this case and others, I just observe my fish to judge whether they are struggling. They sure didn't like that 75% water change, but I felt like I had to do it, plus the mini-changes I've done following up. Up 'til this, I've had a pretty good read on my tank - for the fish, at least; it was the dang plants that started this mess!
BTW, I did a 20% water change late this afternoon, and my fish - including my angels who were looking quite distressed twelve hours ago - are all looking really perky. Water reading tonight (after a wee trip downtown to celebrate Canada's hockey and bobsleigh victories
): Ammonia a little bit lower - definitely no higher than 0.5mg/l, nitrates 10mg/l, pH 6.8ish
I'll see if I still get a higher reading on ammonia tomorrow - if so, I'll invest in that Ammonia Alert to make sure we're all okay.
Fingers crossed for my lovelies, and thanks to all for your advice and concern. Please keep it coming!