Water Change /Calcium/PH Drop

[ScottB]

On my new tank, I did my first significant water change yesterday, since I reached stable state. (not my first, just first >5% change since I considered the tank ready for stocking, which has been about a month.

The tank (60g) is lightly stocked (4 chromis and a clown) and started with ALk of 11.2, pH wavering around 8.1-8.2, SG 1.025, temp 77-78, CA ~330.

I had premade salt water for the last couple three weeks that tested out at 1.025, but I failed to check the pH or Alk from that batch. Using the last of that batch, I did a > 20% water change.

Immediately upon completion, my pH began to drop, and has continued for the last 36 hours except when I am dosing ALK. Currently CA is <280, Alk 11.2, pH hovering around 8, but my graphs show it trending downward.

I have made a new batch of saltwater with the same salt and tested it out at pH 8.2, CA ~350, and Alk 8.5.

When I cleaned out the FSW tub, there seem to be a general coating of some kind of precipitate. I must now assume was calcium. So this leads to a few questions:

What would cause calcium to precipitate out of a garbage can full of fresh sea water (Red Sea Coral Pro)?

How did (or did) low calcium negatively effect pH when ALK was in the optimum range? If it did not, where else should I look?

If the tank is relatively new/clean, and well maintained, and Alk is >10, how di I get pH up and keep it there?

Any help would be appreciated.

 

[Randy Holmes-Farley]

Overall, I don't see much concern, except a need to boost calcium if that last number is accurate.

I'd say that the calcium drop was probably random testing error results. It wouldn't have dropped much from the 20% water change.

Many salt mixes have some calcium carbonate precipitation in them, but that doesn't drive down the calcium much. There is a lot there, and there generally is not enough carbonate present so that even if all the alkalinity precipitated out as calcium carbonate, the calcium will be not drop that much.

The pH is controlled by the alk (yours is fine) and the CO2 level, which is often elevated, especially indoors in the winter time. pH 8.0 is fine.

 

[ScottB]

Thanks for your response. I am dosing 1.1ml/hour Ca during the daylight hours, (but only for the last few days. I think I am going to increase that measurably over the next little bit to get it back in line. Starting with another test.

I still don't really understand why pH got so depressed. I will admit to a higher light schedule and more intense light over the last several days which could affect pH, but the pH drop started coincidentally with the water change.

 

[bertoni]

I'm not sure, either. As long as the problem doesn't happen again, I wouldn't worry much, though.

 

[Randy Holmes-Farley]

Closed windows often causes a drop in pH. Did it finally get cold ennough down south to do that?

 

[ScottB]

Closed windows often causes a drop in pH. Did it finally get cold ennough down south to do that?

Actually, over the last few days it was warm enough to run the air a little bit. This weekend, however, promises to be different.

 

[Randy Holmes-Farley]

OK, so you probably had closed windows to run the air conditioning? That will also allow indoor CO2 to accumulate and drop CO2.

 

[ScottB]

This thread got me thinking, my cabinet is primarily closed, unlike a lot of cabinets that are open in the back. I just now dropped in a little 4" fan evacuate the cabinet (through some three inch holes that are in the bottom and back. This will likely help keep the tank a little cooler, and provide a source of fresh air. Maybe this will buoy/stabilize the pH a bit.

 

[Randy Holmes-Farley]

It may. Is there a skimmer in the cabinet? That and the tank top are the two primary ways our tanks are aerated.

 

[ScottB]

The skimmer is in the sump in the cabinet. Actually, I wonder if it would make sense to route the skimmer air inlet outside of the stand? It would sure be quieter.

 

[Randy Holmes-Farley]

That would be a fine choice.