Water turned alkaline, help!!!

[Rugrat]

Hi this is what happened to my 3 feet tank.
Sunday afternoon: saw my tiger snail on the floor. How did it get out? I put it backed.
Sunday night: saw 1 SAE getting aggressive. It chased after 1 lampeye. In fact, 1 lampeye switched off its ‘spot light’.
Took no actions.
Monday night: Casualties: 3 rainbow paddis, 1 golden algae eater, 1 lampeye and 2 octocintus dead.
Water shows suspended white particles. Very little amount. You need to look carefully in order to see it.
12.50am: Immediate/late action: Checked Ph. Water turned very alkaline. Hardness is at 2.
1 am: Add black water to make lower the PH. Add bio-cycle add too.
1.30am: PH is still not down. I did a 50% water change. Careful not to lower down the PH too fast.
3 am: Asleep.
8.30 am: Casualties: 2 Cardinal Tetra, 2 pencil fish and 1 rainbow paddis dead.
At home now. Hope no more casualties.

What could be the cause of these?
*Is the bio ceramic ring out of date (10 months old)? Or do they have an expire date in the first place?
*Could accidental use of water that include very little amount of soap or detergent be the cause of this?
*My CO2 is giving me trouble lately. Sometimes, stop giving out bubbles after a few minutes. I have to adjust the valve again. I just to a bigger 3.5L tank. Do I have to turn the main valve to maximum? I just turned the main valve a little, then I control the smaller attached valve.
 Usually, I add in half a tablet of Iron for the plant. This time, I added in one and a half. Will iron increase, its PH?

Thanks for reading and helping.

[juggler]

Soap? It's a absolute no-no in tanks, no matter how small an amount.
Perhaps it is the cause of the pH rise?

Perhaps you need a few frequent large water change to get rid of traces of the soap. And in the mean time, salvage your fish (if you can catch them) into clean water.

[Aeon]

From what you said, are you having problems adjusting the regulator / valve? lack of CO2 could be the problem of the increasing pH. The Bio Ceramic rings could be a cause also, what other KH increasing elements do you have inside? if none, could be that teh ceramic rings are KH-increasing.
Soup is a absilute no-no, as juggler said. It's poison.
Ammonia is also alkali so you might need to see if it's an ammonia spike. Have you cleaned the filter lately?
Most soap are alkali, I tested many brands with litmus when I was in primary school.
Check your soap to see if it's alkali. Boil some red cabbage to make some red solution, soak paper (sketch pad paper is good, must be absorbent) in the red juice until the paper is red / violet. dry then touch the wet soup with it. Bluish = alkali, yellowish = acidic.

[bclee]

Rugrat, what is your pH reading?

I doubt the pH has anything to do with your fish deaths. You might have missed something. What changes have you made recently? e.g. adding new fishes, clean filter, major re-scaping, etc.

What iron tablet is that you are adding?

BC

[Rugrat]

Went home today. Casualty stabilize to one cardinal tetra.
Did a 25% water change this time.
Tank water 7.0.
Checked tap water out of curiosity. Gosh. Tap water was 7.5. Stayed in Geylang. Did the recent circle line MRT got anything to do with it?

Perhaps should not have changed water on Saturday. I believe tank water was about 6.0 before the 30% water change on Saturday. Usually, during water change, I did add a 5ml of tetra black water for about 35litre of fresh water. This time, I didn't.
I add 1 & 1/2 tablet of Denere iron tablet. Usually, I only add 1/2 tablet. This time, I added 1 & 1/2.

Perhaps is a combination of everything.

Could also be CO2 not working.

Added 5 wild lampeye on Saturday. Another 5 on Sunday.

No major landscaping done. Planted some stem plants on Saturday night.

Cleaned external dolphin filter also. Shaked the Dr Aqua bio ceramic ring (8 mths old & very porous) in the dirty water. Did not wash the ceramic ring or the container with any tap water. Then, throw away the dirty water. Connect back to the tank, and let tank water flow into the filter.

I used fish guard to declorinate and de-choramine the water.

Tank contain 2 small to medium sized driftwood and 2 small to medium sized larva rock.

Thank you very much for helping.