nitrites STILL won't go away

[RTR]

The iffy range of BW is where the types of bacteria that perform biological oxidation of ammonia through nitrite to nitrate change over to SW species, entirely different bugs.. In FW and BW up to full marine (SW), we rely on bacterial oxidation to render ammonia waste (from fish and inverts and aerobic bacteria) relatively harmless by so-called "biological filtration". Some full SW tanks do also, but in SW there are more effective techniques available. When we raise salinity/specific gravity, that range is where we have to be very careful, plus a bit on each side of that range if there is any uncertainty of what the salinity really is. In that range small changes can kill off FW bacteria, so you can lose FW bugs before the SW bugs have sufficient number to take over the job.

Fish can usually be drip-acclimated in a matter of hours if needed. Bacteria cannot. We have to allow more time for the new required colonies to grow to sufficient size and numbers to take over the whole load. That requires time in days, not just hours.

Testing is separate matter. Colorimetric testing - use of liquid-based tests read by color change or intensity is also affected by salinity. Even if the same test reagents (the liquids or powders used for the tests) are used for both FW and SW, the colors read will likely be different. That is because the higher mineral (dissolved ions, commonly called TDS - total dissolved solids) content of BW and SW can and does affect the color intensity. So, different color charts are and must used to interpret the results. The effect of that difference is not purely linear. For any brand of test it will not be identical with other brands. You have to ask the manufacturer of the test as to what salinity or specific gravity you have to change from the FW to the SW charts. At the tricky range - from just below to about I/2 full SW, it will be different and sometimes difficult to read accurately.

If that does not help or clarify the problems for you, speak up and I'll try to explain it again. This is something everybody but chemists have problems with - don't think that it is just you. This confusion is all but universal in the hobby.

HTH

[sevenyearnight]

No, RTR, that is more than perfectly clear. That is what I thought you meant, and I wanted to make sure I did indeed understand it correctly. Thank for the more detailed explanation, I'm glad to learn new things!