chemistry/ph question

[drm]

HI--
Just finished a second cycle with my 30 gal tank, second cycle occurred with addition of my live rock. My primary question is that my ph now seems to hover at about 7.9 and is not correcting. (checking 10am or so)

Using IO salt (however 3 months ago actually started with another brand, Red Sea maybe? and my PH was always 8.2, and was initially with tap water). I changed salt brands a few days before cycling with my live rock, and I did a lot of water changes during the cycle with the new salt. Not sure if the salt change or the cycle forced the ph down, but my pre-mixed salt is only about 8.0 also. I'm hearing from people to not add buffers, etc... I did try it some but would only get a temporary increase and back down later.

Tank has 3" sand, 30# live rock, 20# established base rock, cleaning crew, no fish.

I have lots of water flow/current. I was running carbon but I took it out about a week ago (for now). I'm not running a protein skimmer yet because I haven't figured out how to put it together, but hope to have it in soon. (Bought it from someone else with no instructions.)

I have Temp 80, ammonia 0, nitrites 0, nitrates about 7.5
Ca=400 or so, Phos=0.25 (0 in pre-mixed water), Alk="high" although I don't have a number.
Have done tests with two different brands and received similar results.

Last... I don't have a RO unit yet, but I am using DI water. While I do plan to add an RO unit based on everyone's recommendations, I'm not sure how that would improve the PH over the DI water?

Thanks for the wealth of information on this site! and thanks for your help!

 

[fishfreek]

When you check your PH how long are the lights on for?

Different salts will produce slightly differnt PH values based on the amount of buffering their mix contains.

 

[malkore]

Feel free to start a thread (maybe down in the Hardware forum) on your skimmer...someone here can help you get it assembled and working.

I'd say don't mess with buffering. I would get a different test kit for Alk that actually gives you a mg/L, ppm or meq/l reading...since low, medium and high doesn't really help
I'd say you probably have enough alkalinity that you shouldn't need buffers.

My tank was the same way at first, 7.9 with IO salt. After a couple weeks, and switching to R/O D/I water from tap water, my pH corrected itself, and never goes below 8.1

 

[drm]

The lights go on about 7:30 a.m. and I've typically been checking the ph around 10 or so. Does the RO part of RO/DI make a difference over DI water alone? Seems like the ph was better on the old salt with tap water. Should I change back, or just wait it out? Do something (besides maybe RO?)? Do nothing?
Thanks...

 

[quarryshark]

Try checking it in the middle to the end of the lighting period and see what it is.
May want to change salts. I use oceanic and my change water PH runs about 8.2.

 

[drm]

Checked ph 7:30 p.m today and was still about 7.9
If I do change salts (again), is it right to just do water changes and add the new brand with each change? Does it matter how fast I do this (10%-20%, every day/week etc)?

A hardware forum (in response to malkore)... hmmm I didn't see that forum. Thanks, I'll look there.

 

[jackdp]

Have you done any water changes since the tank cycled the second time? The acidic by products of the cycle will inevitably drive the pH lower. Though IO can run a little low on the CA and Alk side it should still mix to about pH=8.2 or so. I would do a few water changes with the IO over a week or two and monitor the pH, I suspect it will rise. Also, check the pH near the end of the tank's photoperiod and see what you get. Just to be on the safe side, check the pH of the freshly mixed SW before a water change and make sure it is 8.0-8.3. HTH

 

[drm]

I did quite a few water changes during the cycle, hoping to preserve as much live rock life as possible. Since cycle completed (when ammonia and nitrites hit zero, nitrates fell below 10), I have done probably 2 water changes. I guess I can try to do a few more and see if it improves.
Thanks.

 

[blorkiemom]

I use IO with RO water and get a pH of 8, also. I'm starting to think it's the salt, after all . . .

 

[jackdp]

If you've been doing water changes you should've seen some improvement. It could be the salt, or it could be a lack of oxygenation. Do you keep windows open and get fresh air into your house or the room where the tank is. If there's a high concentration of CO2 in your house it can drive the pH down in your tank. Even if the tank gets fresh air, you just may not be getting enough gas exchange in your tank to blow off the CO2 that naturally builds up in a tank, running the skimmer would help with that also. I wouldn't blame the salt or add any chemicals until you've had the system set up, cycled and all the filters, skimmers etc running as they would be normally. ps...to check for the low oxygen theory, take a small dish of water from the tank, measure the pH immediately and then allow it to sit near some fresh air for an hour or so and measure again. If the pH rises significantly then that may be part of the problem...

 

[quarryshark]

Also if you have a glass top, leave it open for a while and see if that doesn't raise it. Power heads pointed towards the water surface can also help to improve gas exchange and also raise the PH.

 

[drm]

I tried your suggestion to check on the oxygen... I left it for about an hour and there was a subtle change in the color, but was still not really even up to 8 from 7.9. Of course, the water was then very cold so I'm not sure how that affects it either. OK, I'll work on my protein skimmer and see if it helps, along with my water changes.
Thanks for the input.

 

[jackdp]

You may want to test your freshly mixed SW for pH and alk. But more importantly, I'd look for another source of freshwater. You said earlier that your mixed SW tested .25 for phosphates, that will lead to algae problems down the road. It certainly wouldn't hurt anything to try another salt brand. I've had good results from Kent Sea salt, IO Reef Crystals and I've heartd good things about Tropic Marin salt.