I have bought some crushed coral today. My Ph has always been 6.8, no problems. I noticed that the fish looked a bit off so tested the water for the usual and nothing appeared wrong, so I tested the Ph and it had dropped to 6.4. I had no idea why it would do that, but I tested the Gh and Kh this morning and my Gh is 100 and the Kh is less than 10 as it only took one drop to change colour.
I have been debating for some time about getting the crushed coral, I went out and got some, but I am unsure as to how much to use in my filter, any help is much appreciated.

I have tested my tap water and it is

Ph 6.5
Kh 40

Do I need to be changing the water before it goes in the tank after a water change, if so how? Can I use Bicarbonate of Soda (?). Im getting confused now, and worried about changing things, I dont want to lose any of the fish. Would it be wise from now on to do smaller water changes, say 25%, instead of 50% and just do them 2-3 times per week?

Sorry for all the questions.

Crushed coral will increase the pH rather slowly, over a few weeks, but once it is dissolved in the water then it stays pretty stable. I don't know of any scientific measure of how much to use but around a teacup full for each 10 gallons and make sure you wash it well first. You should do a water change first because the tap water has a higher Kh than your tank atm.

If you are still concerned about your pH after the water change you could add a teaspoon of bi-carb for every 10 gallons, wait 10 minutes then take another pH test. Repeat this process hourly until you have reached your desired pH level.

I have found once sufficient dissolved coral gets into the water I can do a 50% water change no worries about the pH falling. This may take a few weeks though.

Thank you for your reply, I was thinking of doing a 50% water change today and adding the crushed coral to my big external. Then monitoring it through the week, and next Sunday after water change, add bicarb so as the Ph doesnt change. Hope that made sense, it does in my head!!

Sounds good to me Claire. After a few weeks you probably won't need to worry about the bi-carb.

Thank you, Is Bicarb safe to use? How much do I need?
If I monitor the levels, and my ph gets to 7.2 or 8.3 there is a buffer I can use that wont let it drop, would that be better than the bicarb?
I dont like chemistry, gets me too confused!