Fishless cycle PH fluctuation

[TnMark]

I'm through my first week in cycling my new 135 gallon tank and ammonia is 0 now for 3 days. Nitrites peaked about 2 days ago at 5 and are now down to about 2 and nitrates after being at 12 on day 2, 0 on day 5, 2.5 yesterday are at 5 today. Everything seems to be ok. However my ph is all over the place and the only thing I am doing is adding ammonia to the tank. No plants, no fish, silica sand substratr. The tap water has a ph of 7.2 and is hard (GH 190, KH 107). My ph started at 7.2, went up to 7.8 on day 1, bounced from 7.2 to 7.6 until it seemed to settle at 7.2 on days 4 to 7 (today). Today I measured at 8.2. I tested with my electronic tester and verified with both ph and high ph tests from Aquarium Pharmanceuticals. Is this odd? Can anyone help? I feel I really need to get the ph stable but am reluctant to add chemicals.

 

[wetmanNY]

If your pH is rising, it's a good sign you have carbonates in the substrate. Perhaps it's a white substrate sold for marine aquaria?

There's no reason to add stuff to "adjust" the pH. Especially without any fish in the system.

 

[famman]

If you have a low gh/kh, ammonia can change your ph.
After a fishless cycle;
Your ammonia should be at 0.
Your nitrItes should be at 0.
Your nitrAtes would have started at 0 and increased once nitrItes start to drop.
The only way for nitrAtes to decrease is to water change them out or if you have plants. (or if you're using a de-nitrifying coil).
Once you're sure you've completed your cycle, the ph swings will fall back to your tap water level when you add fish unless you have something in the tank that might raise it such as crushed coral.
check your gh/kh
good luck

 

[JSchmidt]

Your KH is toward the low end, suggesting your water will be somewhat prone to changes in pH in the face of acids/bases. At over 100 ppm, though, you shouldn't be seeing bounces like that.

When you checked pH, did you do so consistently to when you added ammonia (e.g., right before, right after)? Have you added any tap water during this period?

Are you certain the sand is silica? (Sorry, but I have to ask. pH increasing is often a sure sign of some sort of calcareous substance and the sand is prime suspect!)

Some additional thoughts that may or may not be helpful: tap water, especially when cold, can hold carbon dioxide which lowers pH. As the water warms and CO2 is offgassed, the water becomes more alkaline (i.e., pH rises). This could account for some of the increase in pH over the first day or two.

Competing with that is the acidification that occurs as ammonia is oxidized into nitrites and then into nitrates. This tends, in water with low KH, to draw down pH over time, although I'd be surprised if it happened so quickly in your tank. (Knowing the level of nitrates would help here.)

All that being said, I don't understand why you pH would be bouncing around so much unless you're doing water changes. Even if the substrate was calcareous, you should see a steady rise in pH, not advances and retreats...

When I encounter these sorts of conundrums, I get very methodical in testing to try to rule out any variance in testing procedure - testing at the same time every day, drawing the sample the same way, etc.

Sorry -- best I can do at the moment...

Jim

 

[Faramir]

I'd boil some tap water (drives off dissolved gases), let it cool, then test the pH again. This will eliminate or indicate the true pH of your tap water being masked by dissolved CO2.

 

[MP]

Ammonia itself is a basic compound (has higher pH), so, if KH permits, addition of ammonia will raise pH temporarily.

However, two main products of nitrification are nitric and nitrous acids that will push your pH down (again, if KH permits). Fishless cycling involves enormously massive nitrification, so drop in pH is a very real danger in poorely buffered water.

At this time and with water I wouldn't worry too much. But you may consider doing occasional water changes to replenish the buffer during the cycling. Although your tap water kH is not really low, it may, at some point, get fully exhausted.

 

[TnMark]

Thanks all. My sand is play sand from Lowes which is according to the package silica sand (Company name is Silica Products). I have not done water changes and have not added any water and hadn't planned to until cycle is complete. Also no plants yet. Today for the first time I did test after I added the ammonia so that could possibly be the culprit. Additionally I have just raised the temperature of the tank and my lights have been running hot (water temp is 82 in anticipation of adding discus it was about 77). At this point I'll just let the cycle run and hope it stabilizes in the next 2 weeks. Thanks again.