High Alkaline, dead minnow

[LingDiLong]

We have 7 minnows in a 60l tank - we got them a few months ago (I was posting under the name Mrs Gravy and got loads of advice from Eau Rouge which I followed to the letter). Water levels - PH, ammonia, nitrite - have always been fine. This morning I realised one was missing and found it dead, stuck in the pond weedy type plant we have. I checked the water levels and all was fine except the PH which was showing really high alkaline levels. I've done a big water change which has brought it down a little but it's still too high - about 7.6.

So, I'm wondering whether the fish died because it got stuck in the plant and then it's rotting body (it might have been dead a while before we noticed as we were out all day) caused the alkaline levels to rise?? OR did the high alkaline levels cause it to die? If it's the latter what could have caused this sudden spike and how do I get it back down to neutral?

Thanks!

[EauRouge]

7.6 is fine for minnows, they prefer harder more alkaline water than some tropical fish. How high was the pH when you first tested it? What's your tap water pH (leave to stand for 24 hrs before you test it)? What substrate and decor do you have in your tank?

A dead minnow may cause a small ammonia spike but it probably wouldn't have been noticeable in a mature, lightly stocked tank. It wouldn't have caused a pH rise though, prime suspects for that would be some kind of mineral in the tank, possibly a rock, coral sand or some kinds of gravel.

Are the fish showing any symptoms like excess mucus (looks a bit like cobwebs) or are they holding their fins close to their bodies?

[LingDiLong]

Thanks for the speedy reply! Not sure what ph was when first tested, or what tap water ph is - will check that. Last time I checked tank ph it was neutral. We have some gravel in the tank and 2 small live plants, one plastic. A couple of ornamenty things. No symptoms, fish swimming happily and eating well. Even the dead one looked ok apart from the deadness of course! So is it possible for it to have got tangled in the plant and died because it couldn't move?

[EauRouge]

Unlikely, fish are normally pretty good at swimming through plants. It's hard to tell what has killed a fish, you'd need to do a post mortem and all kinds of tests- and probably have some kind of animal pathology knowledge The water parameter changes are a worry, large, sudden changes in pH can put a lot of stress on a fish's immune system so it can leave them open to bacterial infections etc.

Let me know what the results of the pH test is. What are the ornaments you have in the tank?

[LingDiLong]

Oh the usual naff stuff (our neighbour gave us the tank plus everyhing with it) a gone fishing sign, shipwreck and house. We did have another plant but it died. Will let you know what that ph is. Thanks again!