ph, kh and gh levels?

[Lmacbeth]

I added 5 Mollies (2 black & gold marble, 2 silver) to my 10g tank about 3 weeks ago. Ammonia and nitrites were both 0 before I added them and have remained so....
A few days after I added the fish: ph: 7.4/7.8, kh: 6, gh: 9
1-2 weeks later - ph: 8.2, kh: 8, gh: 13

Fews days old tap water - kh: 11 gh: 15

I've done a parital water change every week also.
Why did the ph, kh and gh go up? And is the ph too high for Mollies?

I have 3 plastic plants, one small ceramic ornament and one rock type castle that I bought in the lfs. (Could the castle be increasing the hardness?) It has brown algae on it but only on the side facing the front of the tank. There is some brown algae on the glass too but not much.

I've also noticed that the marble Mollies have become aggressive mainly towards the silver ones and sometimes each other.. swimming at them like torpedos!! Other than this they all seem fine.

I'm afraid I'm not feeding them enough though as I'm wary of overfeeding.... could this be why they are becoming aggressive?

 

[Spy_90]

how did your PH get so low in the first place? from your tap water it sounds like your PH/KH/GH should be higher? To get these levels down you can do a small water change with distilled water every week or so. Just make sure not to make large PH changes with fish in the water.

 

[Lmacbeth]

I didn't do anything.. not on purpose anyway.
I forgot to check the ph of the tap water actually, must do that.

The tank was up and running without any fish or water changes for a good few months... could this result in a low ph?

 

[Spy_90]

hmm maybe, was there anything in the tank? were you adding ammonia? the nitrogen cycle naturally lowers the PH over time, but you should have experianced really high nitrate levels if you tank has been going for months without a water change. hope that helps a little : )

 

[Lmacbeth]

There was just gravel and the power filter in the tank.
I also added some Stress Zyme at some point.
I wasn't checking the ammonia and nitrite levels because I knew I wouldn't get around to adding any fish for months.. so I just let it be, running away.

 

[Spy_90]

hmm i doubt that any nitration was going on then =\
is your power filter a HOB style? Does it flow into the tank causing surface movement? If so you might have built up a lot of O2 over the months the tank was sitting there. A lot of O2 would lower your PH a bit. Just throwin' out ideas =\

 

[Lmacbeth]

HOB?

Sorry if 'power' filter was the wrong description..... ?
It's a fluval 2, internal filter. Like the one in this link but mines a bit of an older model by the look of it.

http://www.hagen.com/uk/aquatic/product.cfm?CAT=1&SUBCAT=107&PROD_ID=01001650031001

 

[Spy_90]

HOB, hang on back =)
i'm out of ideas as to why your PH would drop like a brick suddenly =\
Hopefully it was just something related to it sitting around, and the tank will stabalize.