Please HELP! MY TANGS LIFE DEPENDS ON IT! :)

[tellico tornado]

OK, my alk and PH both were a little on the low side about two weeks ago. I went out and bought some Seachem Reef Builder to raise the ALk, this fixed the problem but the PH was still hanging at only 8.0 Well, i thought that would be ok and that the Reef Builder would raise the PH by raising the ALK..... wrong. Today is the first day in two weeks ive had time to test my water, everythings fine, except my alk and PH are WAYYYYYY tooo lowwwwww! PH is reading below 8.0 its around 7.6 and alk is just off the charts low. I added another dose of Reef Builder about 10 minutes ago. What is the best way to maintain a steady level of Alk and PH????? Also, could this be why my blue tang died lastnight and why my Yellow tang is lookin really sick?
FYI
120 Gal Tank
Fluval 404 Filter running only bio media and the sponge [no carbon]
85lbs of Live Rock
Arag Sand and Crushed Coral mixed bottom
1 yellow tang
2 Damsels
1 Six Line Wrasse
250 crabs
100 snails
Devils Hand Finger Coral
Frogspawn Coral
Ivyopora flowerpot Coral
Green Open Brain
Green Stripped Mushrooms
4 power heads
Power Compact Lights
uhhhhh cant thing of anything else
I do NOT do water changes, just add top off water when needed.
Any help will be greatly appreciated! Thanks

 

[adrian]

What test kit are you using? what time of day are you testing the pH? Proper pH is essential to fish health and if it drops too low it can shock fish and the result is often death. I would first make sure my test was accurate, and then, if needed, take steps to correct the pH with a water change using a quality salt and a buffer designed to boost pH

 

[austin01]

I have had great success with a product called Restore. I maintains my pH, alkalinity, and calcium levels so rarely do these perameters ever fluctuate. My lfs sells this product but you can also purchase online at <a href="http://www.r-e-e-f.com" target="_blank">www.r-e-e-f.com</a>

 

[frankl15207]

There is something in your tank bringing the level down that far. If you have a filter, make sure it is clean.
Do you have sand stirrers? Is the sand packed or loose? Is there debris somewhere in your tank that you either see or can't see because it's caught under something?
If you can't find something along that line, take a powerhead and move it around the tank and through your rock manually like a reverse vacuum cleaner and see what it kicks up.
Water changes with that kind of bioload would be a good idea. Do 10% at a time and pace them over a number of days. Even normal PH dropoff in a saltwater tank should not go below 8.0. Your stocking shows enough sand and rock to buffer the PH.
Something acidic in the water is causing this and it is most likely something decaying that you aren't seeing or removing.
Adding boosters may help in the short term, but you need to find the cause to get things stabilized.

 

[q]

Also reef builder will gradually affect the ph you need something faster. I would try eather marine buffer also by seachem or an additive that will directly raise ph. I have never added anything that would raise ph specifically raise the ph so make sure it will not harm the tank before you go dumping something in because you read it on the internet.
BTW marine buffer adds the carbonate and raises the ph to 8.3 but not over.