ph drop 7.6

hi guys
i have developed a problem with ph and dkh that i cant fathom out.

tank was stable for about 6 months with ph of 7.8-8.0.

i decided i would try and raise to about 8.2 so i bought tropic marin ph/dkh buffer. that did work adding it over the course of about 3/4 days and all seemed fine.
just after this i had to get salt but couldn`t get what i have always used before which was d+d so i thought i would try tropic marin instead.
so i made a new salt mix and done my water change as usual checking ph and salilinity before adding. That was just over a week ago and also at that time i added a bag of purigen to try and reduce my nitrates which are and always have been 5-10.
2 days ago i topped up 2.5ltrs of fresh ro water to compensate for evaporation over the previous week.

then this morning i noticed alot of brown skum on the surface of the water which has never been there before (like specs of brown sand),so i checked ph and was shocked to see it at only 7.6 ish and also my dkh is editonly 6.6 dkh dont know how i got this reading earlier), i have now checked it again 3 times and it is actually 12.8 dkh so it has risen alot.
my readings today ;

tank 240ltrs
no3 5
no2 0
nh4 0
ph 7.6
dkh 12.8
temp 25
salinity 1.024

i cant see any thing that has died off .
the only differences are alot of brown skum which i have never seen before and my star polyps dont look too clever.
fish, shrimps seem ok at the moment.

so the only changes i have made starting 2weeks ago
1. added yellow tang and blenny
2. added purigen
3. changed salt from D+D to tropic marin
4. did 10ltr water change with new salt 10 days ago
5. topped up with 2.5ltrs fresh ro 2 days ago
6. added some ph buffer 2 days ago cus noticed ph had dropped to 8.0

could it be the change in salt ??

 

The pH swing my be due to low oxygen levels in the house. If your home is closed up for winter then CO2 builds up in the air. Try to get fresh outside air to tank. I have air pump outside that brings in outside air to 4 air stone in sump.

 

thanks otty
should i try to bring the ph up with buffer or water change.....or both.

i am checking ph now

 

You haven't said what your Mag and Calc are. Without those numbers I would not be trying to raise one or two elements if the chemistry balance is off. I will give more thought to the brown scum which is unrelated to the things mentioned.

 

i didn`t realise mag and cal had an influence on ph that much.
i am not into corals very much yet, only fish and a couple of softies at the moment.

 

If you are getting a lot of surface scum, you need to arrirate the surface water more. Aim a powerhead up towards the water surface.. This will also help increase your PH since it will increase dissolved oxygen levels.. Unless your house is full of co2..

Try what Otty said too.. Just make sure you set the air pump outside of the house and run the air line into your sump. Using indoor air could just make it worse if there is too much co2 indoors.. Be prepared for a salt creep mess using airstones..

 

Please post Cal, Mag and Salinity also..

 

salinity 1.025

getting a cal test kit tomorrow and calcium supplement.

from what i understand the buffer that i have been adding to try and get my ph from 7.8 to 8.2 has most likely caused my alkilinity to rocket which in turn could have effected my calcium and ph.

 

Try getting fresh air to the tank.

 

pH fluctuates through the day. The net consumption of carbon dioxide during the daylight hours, leads to some aquariums to become deficient in CO2 during the day, and the pH rises.If you are having dramatic fluctuations you can aerate the aquarium water to degass excess carbon dioxide. Also try using a salt mix with a naturally higher buffering capacity like Tropic Marin or add buffer to raise your alkalinity to help reduced the pH swings.