Aquarium ph is very low compared to others?

So im doing a fish in cycle with a betta in a 5 gal (short story he was gifted) and I had him for weeks but the cycle wasn’t starting I test every day and ammonia nitrite and nitrate are all 0 so I checked my ph but wasn’t worried because my ph has always been 7.6 in every other tank but when the readings came back 6.6 I’m confused because I have no driftwood etc and my waters always been hard and high alkaline but in this aquarium only it’s the opposite

 

Hm,
How is oxygenation? CO2 causes pH to drop

 

Hm,
How is oxygenation? CO2 causes pH to drop

This is a silly question but does that mean like Is there an air stone etc? cause I do use a sponge filter so I think it’s good

 

yea, generally oxygenation is referring to surface agitation

Sponge filter should be fine for oxygenation.
Do you happen to have a gh/kh test kit? Low kh would make you more prone to pH swings. Also, if you test the other tanks right now are they still at a high pH?

 

yea, generally oxygenation is referring to surface agitation

Sponge filter should be fine for oxygenation.
Do you happen to have a gh/kh test kit? Low kh would make you more prone to pH swings. Also, if you test the other tanks right now are they still at a high pH?

Yes I have a kit and that makes sense I’ll test both when I get home from work and I’ll test my other tanks when I get home
Sorry I don’t really know how to test kh I read the directions and after 2 drops it turned yellow that’s all I know
Now my big goldfish tank which is normally 7.6 is now 7 of ph this is crazy
When I said big I meant 20 gallons