pH at 8.4 - should I worry?

[pinkpanther]

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[NancyD]

Stable pH is more important than a specific number but it may be the shell(s) +/or something else raising it so much higher than your tap. Do you have a TDS meter? That might help... for ~$20 USD. Shells can be a death-trap for hiding fish as they grow, I'd remove them. Wood, pH neutral rock or pvc pipe would be a safer choice. You shouldn't need a buffer, they can lead to pH bounce, much more stressful to fish than a stable pH. What substrate do you have?

[Diana]

Fish are more concerned about the mineral levels in the water, the pH is secondary.
Test the GH and KH. If these are too high, then start by lowering these (slowly) and see what the pH does. 8.4 is a bit too high.

Here is how I have handled this situation:
Make up new water with lower GH and KH, and run it through some peat moss to make sure the pH is low.
Do water changes such that:
The GH and KH drop no more than 10% when the new water is well circulated with the old.

If you need to do a large water change, then the GH and KH of the replacement water should not be too low.
If a small water change is OK, then significantly lower GH and KH is OK, and the small water change will result in not much change in the GH and KH in the tank at any one time.
A few days later do another water change, that will drop the GH and KH another 10%. Keep this up until the GH and KH are in the right range for the fish.

If you can post the current water parameters in the tank I may be able to set up something of a schedule of water changes that will slowly, safely get the mineral levels lower.
GH
KH
TDS
NO3
other tests.