Parrot Cichlid aggression????

[sharper]

I have a pink Parrot Cichlid and an Oscar that is about twice the size together in a huge tank. They have hung out together since the day we got them. They seemed to be the best of friends and were attached at the hip.
Earlier this week, we did a water change and I rearranged the plastic plants and moved this stone wall from the middle of the tank to the corner.
In a few days, I noticed some aggression between the two, but nothing to be concerned about. The next day, I saw our Parrot was starting the fights. She/He would keep behind the rock wall as if it was his own territory and whenever the Oscar would come around, the Parrot would try to attack him.
Of course, the Oscar doesn't take much of this and they go at it. I haven't seen them together since. They keep fighting, which is so disappointing.
Our Parrot is about 6-7 inches long, and our Oscar is about 10-12 inches long.
I thought it may be the rock wall must of created a "space" for the Parrot to guard.....but I thought Parrot Cichlids aren't like this?? I thought they were tame and calm.
I decided to check the water and realized that the PH had dropped dramatically to 6.2 over a course of a week. I have no idea what made it drop like that, and I've never had a PH problem before. I am slowly trying to bring it back up, and putting some stress coat so they could heal from their wounds. The Oscar only has a little scratch on his head, but the Parrot has scratches all over his face. I'm really worried about it. And I hope getting the PH back up will help with the aggression.

Has anyone else had an aggressive problem with a Parrot Cichlid? Is there anything else I can do?
Thanks

[Rbishop]

The wall being in the middle probably was giving them each their own space and breaking the line of sight.

What size tank is this? Other fish? This isn't the same tank(s) in your of other posts?

How long has the tank been operating for and how long have they been in it?

Exact ammonia, nitrite and nitrates? pH and same readings on your tap water?

[sharper]

Well I got a video of it happening, and I got a pic of the rock wall to show that it's not that big, it's only 6 inches tall.
But once I can actually find the cord to my dig cam, I'll upload it so you can see it.
Also, I've noticed that the Parrot has started digging a hole in the gravel behind the rock, a couple pieces of gravel at a time. We figured he's gotten too obsessed with it, so I decided to take the rock out today to see what happens. I stuck my hand in there to grab it, and the Parrot tried to attack my hand. This is so unlike him/her! I'm sure it has to be the PH that is perhaps stressing him out. But it seems like we can only raise it slowly. We have some PH buffer for our Marine tank, could we perhaps use that?

They are in a 55 gal tank, and hubby says they aren't as big as I said they were in my original post. The Oscar is about 8 inches, and the Parrot is about 5-6 inches long. We've had them for about 4-5 months now, and they were originally introduced together at the same time. I do have a silver dollar in the tank too, but they don't mess with each other, he keeps to himself. I also have a pleco that is in there too.
I think my past posts say that we had a 30 gal, but that crashed one night and we had to get rid of the livestock in that tank.
We have bought a new one and will be getting it up and running pretty soon, so we are thinking about putting the Parrot in there by himself.

Water params:
Ammonia has always been good, today it reads .5
0 Nitrates
Today's PH reading is 6.2
Tap water PH is exactly at 7.0

We might do a big water change today.

[DeputyChiefJR]

You really should upgrade the tank, the oscar will need at least a 150g...you might want a 200 if you don't want territory issues...

[Tigris7]

I can relate. I have a tankful of African Chiclets that all got along when they were smaller, but one by one, I have had to seperate them all by using 'eggcrate' (used to diffuse light in elevators...gert it at HomeDept in the lighting department) to compartamentalize my tanks. They can still see each other through the eggcrate 'walls' and they talk **** to each other, and even try to lock lips to fight through the grids in the walls. As far as I can tell, chiclets, at a a certain age, simply become territorial and aggressive towards any intruders. My tank now resembles a jail with a bunch of cells, but they still seem happy. It's the only way I could make them not kill each other. BTW, I have a 100 gal tank and then added a 55 gal to spread them all out.