Water Chemistry Questions?

[medicreefer]

First of all, thanks Lee for your help with my other posts. Now I have more questions for you... Sorry to have so many questions in the last few days but, being new to this hobby I keep coming up with more stuff to ask.

So, I've been reading various forums and there seems to be a consensus from some experts and others more knowing than myself, that one should always aerate and buffer any RO/DI (and I'm assuming also distilled) water used for reefing. This apparently applies to both top-off water and water used to make saltwater mixes. The idea is that because RO/DI water is so depleted of any ions and buffering capacity, and because it is very low in pH, with high carbonic acid and nitric acid levels, if you don't aerate and buffer it, it taxes the buffering capacity of the tank (or salt mix) as the carbonic and nitric acids "eat up" the alkalinity, leading to low system alkalinity.

I understand the need to aerate to drive off CO2 and so always aerate my water for making up new saltwater. Starting today, I'll also drop an airstone into my top-off water bucket too. That problem is solved. My real question has to do with adding the buffer to top-off water.

Assuming that basically only pure water evaporates from my tank while the ions and other disolved components that make up saltwater stay behind, if I top off with pure distilled water I'm replacing just the water that evaporated right? Now by adding a buffer, which is usually sodium bicarbonate to the top-off, I'm adding more sodium ions to the system (which never evaporated to begin with right?). So, over the long run am I not adding too much sodium, causing it to rise in relation to the other ions that make up saltwater? This would shift the balance of ions in my tank away from natural seawater over the long run as my Na would rise, particularly in comparison to Cl based on my understanding of the chemistry involved. I know people have a similar problem with long term use of calcium-chloride to boost calcium levels. They end up with unnaturally high levels of chloride versus sodium and it messes up their params. Wouldn't the reverse happen adding buffer to top-off water? (PS I'm not worried about the carbonate part of the equation because I understand that part of the sodium bicarbonate is easily used up by my livestock, however, the Na ions are not.)

I love this hobby but the more into it I get, the more I think of this stuff. I hate doing things just because somebody says so, without understanding it for myself.

Thanks.

[leebca]

Don't worry about asking. I wish more people did the asking before they do the doing. If that makes sense!

I've not heard about aerating top off water. I see no need. I have not heard of adding anything to top off water, since adding to it would only increase the ions in the DT when it is added. This makes no sense.

As far as using aeration in newly prepared salt water, I'm against and have a short mention of that here: How to Make a Successful Water Change

So what is perhaps really going on? I think people have forgotten why they make alkalinity, calcium, and magnesium adjustments. It is these three things that make up the buffering ability of the water AND what need to be balanced.

You see, hobbyists are given ranges of where to keep these three, but in reality they don't just need to be in range, but they must be balanced against each other.

I have provided the proper balanced numbers in this post: What is Water Quality

If the water is properly balanced, then there is no need for pH adjustments. Alkalinity, calcium, and magnesium need to be kept in balance to keep the buffering ability of water strong.

Then, when water evaporates -- the pH remains controlled; and when salt-free water is added back as top off -- the pH remains controlled.

The actions you've posted as others' recommendations, sounds like they have missed the basic step of having balanced and properly buffered water. Adding chemicals to alter one without regards to the other two is just plain wrong.