Water Chemistry - ph and hardness

[Danh]

I'm going to resurrect this.

All of the issues I caused myself with the crushed coral in the sump and cooler water change water had stabilized but I frequently saw unexpected behavior with the fish. Lack of appetite was probably the most frequent symptom.

While I had this tank I set up my first reef tank as well. I wanted a tank in my bedroom and set up a 93g cube reef. I eventually got an Apex controller for it and could monitor ph in almost real time. The norm was around 8.2 with very high alk levels. Even with very hard water, I noticed a slight ph drop when my kids got home from school or in the evenings when the door to the bedroom shut for an hour or so.
CO2.....
Apparently my 3000 sq ft house is very air tight. More people, shut doors, other CO2 creating activities with the bedroom door shut... would get the ph down to as low as 7.8. Then I found that the gas oven on the other side of the house would hurt it. And the gas fireplace in the living room on for an hour caused a ph crash.

It's crazy what atmospheric CO2 in our houses can do to hard reef water... I'd hate to see what it was doing for incredibly soft tap water. I think that was my problem. I think consistently using the crushed coral as well as an air exchange with fresh, outdoor air, would have been the way to go.

I never knew so much was going on with my ph!

 

[David R]

Interesting, I guess there is a trade-off between insulation to keep your air warm and ventilation to keep it fresh. The ocean acidifies as the CO2 in the air increases and is absorbed, so I guess it shouldn't be surprising that the same can happen with our aquariums.

About the coral and soft water being discussed earlier, my tank (and house) is fed entirely with rainwater collected on our roof (common practice in rural New Zealand) so it has zero mineral hardness whatsoever. I too keep fish that prefer soft water and have plenty of driftwood in the tank. I balance this out with a basket of lime chip in the sump, and a bit of beach sand (which is mostly crushed shell) mixed in with the sand substrate. Regardless of water changes my pH is pretty stable around 6.8-7, TDS ~60ppm and GH and KH both very low. In late summer/early autumn I'll regularly do 40-50% water changes without any drastic swing in water conditions.

If you have very soft tap water don't worry about the pH as the lack of buffering means it will easily change, and also that the change will not be anywhere near as troubling to the fish as it would if the water were hard. I read up all about it when I set the tank up four years ago, and as best I can recall the gist of it was that the pH change itself isn't what bothers the fish, but how that change relates to the hardness and conductivity. Going from 5.5 to 6.0 pH with very soft water represents very little change because of low buffering capacity of the water, but with hard water changing from say 8.5 to 8.0 pH would represent a much more drastic change in water conditions.

I never liked chemistry at school, so anyone with a better understanding or explanation feel free to step in and correct me if I'm wrong!

 

[Danh]

I don't think that's exactly right. Low hardness means low buffering capacity and buffering capacity is the ability to stabilize the ph. It seems unlikely that a ph of 6 can drop to say 5.5 due to co2 and low buffering capacity but I never watched the ph that closely on that tank.

I've killed a few more fragile fish before, while a couple of people in the area that I knew that were able to keep them had crushed coral reactors on their tanks. I am certain that even my pbass were showing ill effects of ph drops that were probably affected by CO2 in the house.