Can’t keep pH up in a new tank!!

[virginia reef]

I have 2 new tanks (couple of weeks). All LR and LS came from two other tanks established over 2 years each. Had a minimal cycle-ammonia peaked at about .25 to .50 and nitrite never showed a reading. I have been adding Kalk several times a day for several days. The pH rises as much as .2 but always seems to fall back to its previous level. I have also used Kent pH buffer a couple of times. I use DI water with Kent Salt. All of the livestock seems healthy except for the newest arrival- the Blue Hippo Tang. He appears to have a small case of ich. Just got him 48 hours ago by mail with the cleanup guys.
Should I be concerned about the low pH? Will it rise as the LR and/or LS contribute? I plan to add a drip system to the 90g system to dose Kalk rather than add it in larger amounts manually. What else can/should I do?
The 55g is only to hold the LR till the hair algae disappears. I plan to add the LR and all livestock to the 90g at a later time.
Following are my two setups:
Size:90g
LR:95lb
LS:50lb Live Caribsea Aragonite on top of 150lb new Southdown & 40lb new Caribsea Aragonite
Temp:79
Salinity:1.0235
Calcium:350
Alkalinity:180
PH:8.0
Fish:Midas Blenny, Orchid Dottyback, 2 Percula Clowns with host Anemone
Inverts:50 Astrea Turbos, 40 Hermits, Coral Banded Shrimp, Peppermint Shrimp, 2 emerald crabs
Corallate, Open Brain, Bubble, Candy Cane, Pipe Organ, Clove, Zoanthids, and Mushrooms
Filtration:Seaclone Skimmer in sump, return pump, 2 power heads with wavemaker in tank
Lighting:2x175watt MH 10,000K, 2X65watt PC Actinic
Size:55g
LR:70lb with hair algae
LS:No substrate
Temp:80
Salinity:1.0235
Calcium:350
Alkalinity:?
PH:8.0
Fish:Blue Hippo Tang
Inverts:50 Astrea Turbos, 65 Blue Leg Hermits, Small Hitchhiker Crab (emerald?), Lettuce Nudibranch
Coral:Couple of stray Zoanthids
Filtration:2 power heads in tank
Lighting:2x25wattfluorescent

 

[pudd'ntang]

Usually your PH will drop when your ammonia
and nitrite levels are high, check your water readings. Also do a water change if necessary if they are high. Your PH should stabilize.

 

[fshhub]

check your alkalinity, calcium alk and ph all work together, they all need to be in line in order for the others ot maintain properly

 

[adrian]

How old are these tanks? What test kit are you using? What time of day are you checking it? Be carefull adding large amounts of kalk to your tank, if your adding enough to raise the pH, your most likely adding too much, kalk dosnt work very well when its not slowly dripped, and its caustic and pH swings can be deadly to your fish, it dosnt work very well too boost levels either. If there indeed is a problem I would do a water change as mentioned, I would also stop using the kalk for a while and see what happens. HTH

 

[broomer5]

Keeping a new tank at all the right levels is normally a little tough.
It takes awhile for a new tank to become stable.
If you want though - as your tank's are cycling,
Try this ....
Mix up two small batches of new saltwater.
Maybe 5 gallons buckets each is fine for this experiment.
In one batch - mix the DI water and saltmix as you normally do - and measure the pH and alkalinity.
In the other batch - prior to mixing in the saltmix - aerate the DI water only overnight with a powerhead or airstone.
Then the following day ( 24 hours later ) mix in the salt.
Measure the pH and alkalinity.
As I'm sure you know, DI water is deionized, mostly stripped of all ions, and normally has very little carbon dioxide CO2 present.
Aerating it overnight allows the DI water to become somewhat saturated with CO2.
(CO2) + (H2O) yeilds (H2CO3-) bicarbonate + (H+) hydrogen ion.
This then dissociates to form another (H+) hydrogen ion and (CO3-2) carbonate ion.
Now the DI water is not totally deionized anymore, since it was saturated with CO2 overnight - some very basic natural chemical changes will occur. The water is still very pure, but now has some level of bicarbonates and carbonates present ( without having to add any alkalinity buffers ).
Now mix your saltmix the next day. Mix it to salinity of 1.025
Try it and see what happens.
Pretty cheap experiment - and I'll bet you find that your newly mixed batch of saltwater done in this fashion - will test out close to:
pH 8.3
alkalinity 9-10 dkH
calcium 380
NOTE
My biggest concern here is you state that both of these tanks are only 2 weeks old ?
Do you have any fish/inverts in either of these tanks right now - or is what you listed just a wish list for future stocking plans ?