How low can PH get during cycle ?

[perezbob]

It's been 18 days since my 55 gal began cycling. My PH started at 8.2 on day one as of today it was at 7.34, yesterday at 7.74. I've using a Tetra test kit but most recently have been using a more sophisticated PH meter. I'm getting similar readings on both. My question is, how low can the PH get during the cycle ? Any suggestions ?

Readings as of yesterday were

PH 7.74
Co2 2.4
Temp 80.8
Salt 1.024
KH 8
Nh4 0 (peaked on day 10, started the cycle with a raw shrimp)
No2 <.3 (peaked 5 days ago and has been decreasing)
4" Southdown DSB topped with 15 pounds of LS
20 pound LR
2 X 96 PC running about 5 hrs daily
One modified Skilter running all the time.

I'm using RO water and Instant Ocean reef crystals
Have added 10+ gallons of top off RO water

Thanks for your inputs.
Bye
Norberto

 

[fishfreek]

What kind of water current do you have in the tank? Are you running a skimmer?

Water conditions will go wildly all over the place during the cycle. Having PH drop .9 points seems a bit extreme though.

 

[ReefLady]

Water conditions will go wildly all over the place during the cycle. Having PH drop .9 points seems a bit extreme though.

I agree with this statement, though I don't know that I'd be overly concerned at this point. The acids produced by a cycle can drop the pH considerably.

as of today it was at 7.34, yesterday at 7.74.

Are you testing at different times of the day? pH will be at it's highest at the end of the photoperiod, and at it's lowest right before the lights come on.

To add to FF's questions - is the tank covered (glass top)?

 

[perezbob]

1. The tank is "semi covered", it has a 36 " piece of acrylic to protect the lights from getting wet and salty. It still has an opening of around 6" on each side.

2. The lowest PH was from a morning sample. I'll check after the lights go off.

On a separate note, when do you recommend I do my first water change ? Will this help stabilize the PH once the tank has cycled ?

Thanks
Norberto