Question regarding low TDS

[cresnyk]

Just wanted to do a quick update on this thread since I have all of my meters now and a better idea about where my parameters are.

Both my TDS meter and pH meter have been calibrated and tested on lab certified standards. pH coming out of my tap is 6.25 and raises to 6.5 after aging in a barrel for 3 days. Water tested in my tank a few hours after a 30% water change is 7.2. Could this increase be caused by the amount of gas exchange I have in my tank from surface agitation? I have quite a bit of air going into my tank and 2800gph return prior to accounting for loss from 4' of head plus 6400gph through wave makers (I've been considering adding dorado to my tank so I've increased current, the rays seem to enjoy it as well).

I've found that with my meter the conversion of TDS to conductivity is inaccurate. Since my standards are for conductivity, and the meter is accurate when measuring EC, I'm going to take my measurements in EC from now on. The water dripping into my tank has an EC of 120uS/cm. My tank water a few hours post 30% water change is 140uS/cm.

The rest of my parameters after WC are:
Ammonia:0
Nitrite: 0
Nitrate: 5
kh: 3
gh: 4
Temp: 83F

From these measurements I'm thinking that my water is pretty optimal at present. Is there anything that I should be measuring that I'm not?

There is one sticking point for me. Now, approximates 6 hours post WC, my tank pH has increased to 7.5. Doing water changes is definitely causing pH swings. I've concluded that my substrate is not buffering my system as this is the same result I'm seeing on my tank with no substrate.

I'm currently testing the effect of aggressive aeration during aging my water. This brings me to my next consideration. Which of the following would be best going forward:

1.) Continue doing 30% water changes 2 times a week using aged water (that is, if aeration brings the pH to the same level as my tank)
2.) Reduce WC % BUT increase frequency. Say, 5-10% daily (if pH can't be adjusted by aeration during aging)
3.) Continue doing 30% water changes 2 times a week, but add a buffer such as crushed coral to my filter. At the other end of the spectrum, will peat do anything to help my situation?
4.) I'm currently dripping 50 gallons per day untreated water. Would increasing my drip rate allow me to decrease WC frequency?

 

[cresnyk]

For those interested, aerating aged water raised pH from 6.5 to 7.2 in 1hr.