PH falling

[Lloyd]

my 100gal reef tank has been up and running for about 6 months and generally doing well, I do a 10% water change every 2 weeks, I know this isn't much but I was hoping my caulerpa sump would keep the nitrates down.

Lately my pH has fallen to 7.7 and I'm detecting nitrates at 12.5mg/l -

spec
60 inch 75gal tank
36 inch 30 gal sump (24 hr lighting)
arcadia 43inch T5 4 tube luminaire
2 x 1200 gal/hr powerheads
red sea prizm 100gal skimmer
30kg live rock

I previously had a fish only set and have continued to use my eheim 2327 ext filter (I know it's not doing much but the return provides good water movement!)

3 x anthias
1 x flame angel
1 x regal tang
1 x yellow tang
1 x maroon clownfish

20+ corals including mushrooms,leather,star,xenia,trumpet,plate montipora,yellow acropora (not v happy - prob needs metal halide lighting)
branching montipora etc

I've corrected the pH with the addition of Proper PH 8.3 buffer - do others also need to do this periodically, if so why? and how often?
Any ideas why my sump is not keeping the nitrates at nil

 

[KahluaZzZ]

Maybe because of your prizm skimmer ? The amount of food ? Lack of cleaners ?

My alk dropped a lot recently and yeah i use some buffer every time i put some top off..
it helped a lot
You've tested your alkalinity ?
Do you "clean" your caulerpa often ? If you don't cut the dead white translucent ends, they will decay and acidify your water + add dead organics

 

[wayne]

10% every 2 weeks isn't too bad. Your algae will reduce your nitrates, but as everyone seems to forget, not everything in the world revolves around nitrate, and there are other wastes that need to go somewhere.

To answer your question what is your kH(alkalinity) and how much buffer are you using?
How much is the skimmer (which is hopelessly small for this setup) pulling out? Any algae problems?

The acro might be suffering for any number of reasons. My bet is you have a low kH plus accumulating organics hanging around, forming acids , but not entering the nitrogen cycle (phenols + others don't). Water changes plus more buffer to get your kH to 9 or 10 should fix this.
How much substrate, do you ever 'hoover'

 

[Lloyd]

falling pH

thanks Wayne & Kahluazzz

I've read your comments and done some reading - basically Alkalinity wasn't in my thoughts till now - I was somewhat overwhelmed by the chemistry but I've got my head round it now - the need to monitor kH as well as ph and the need to add buffers wasn't an area I had considered until now - we'll see what happens with some testing and buffering!!

Also I've had several comments that my skimmer ain't powerful enough but then others seem to suggest a skimmer isn't necessary at all - with all that controversy I couldn't bring myself to fork out for a new one.

I take note of the need to try and get rid of more organic matter in filter sponges etc