Weird PH, KH and cloudy water.. Ugh help.

One of my betta tanks has gone wacko over the past 2 days.

I noticed on Friday that one of my betta tanks was looking a bit hazy and there was some stuff on the glass. Saturdays are my water change days, so didn't think much about it. So when Saturday came, I did a 50% water change and cleaned the front panel of glass. Everything looked fine after, until Monday I noticed it was getting a bit hazy again and still waited. Yesterday morning, Christmas Eve, I checked water parameters and to my surprise I had:

ammonia : .25
Nitrite: 1pmm

I did a larger water change then, I'd say almost 75%. Water was much clearer until today, it was starting to get that hazy look to it. This time I checked parameters and got the following:

ammonia: 0
nitrite: 0
nitrate: 0

I was at a loss, but I had a lot of pothos, peace lily and lucky bamboo in the tank. (leaves above water) I removed that and only left the lucky bamboo. I then decided to check the Ph of the water, then the KH.. these are the results.

ph: 6.4
kh: 1 (it was hard to tell because I never got a blue drop, it went straight to yellow) I did it again, same result.

I also noticed that my sponge filter was not producing a lot of bubbles, so I turned the flow up a bit to get some more water moving.

My betta doesn't seem to be stressed, he's acting normal. At this point, I am not sure what to do..

 

Usually when my tanks were at the end of the cycle, they had a crash in PH and dropped to 6.

Could also be a bacterial bloom, which should go away within a few days with water changes.

 

So I took the ph and kh of the tank I have that is currently cycling now, it's been going without a water change for almost a week now. It also isn't planted, just bare tank.

ph is 7.6
kh is 4

I then checked the 10 gallon that I only do about 20% water change on a week. It has pothos, peace lily, lucky bamboo and several other plants.

ph is 7.0-7.2
kh is 2

So I am not really sure what is going on here. My KH on my tap water is right at 4 and GH is 5 (took these from my notes two months ago)

I feel like I need to do another water change on that betta tank, but I don't want to stress him out or even more if he already is.

 

So I did do a water change and I'm glad I did. The nerite I had in there was dead. He was hanging on the back glass yesterday during the water change, so I know he was alive then. He was hanging out of his shell amd didnt move when I touched him. So I'm wondering what happen.

 

I’ve had this after water changes in the past with no ill effects. I have not checked my PH though. I thought it was minerals settling since I have hard water.

 

The past few days it's looked a lot better. I think I have figured out that it's some type of algae, as it was all over the glass and some plants. During the water change, I tried to suck up a lot of it.. keeping the lights off a lot longer than normal has helped.

Reason I think it's algae, is because the 10 gallon directly to the left of it, is starting to develop hair algae as well. Like a dummy, the window between them I had left it open several days so my orchid could get some sunlight.

But still doesn't explain the sudden drop in ph.