Plants, CO2, and PWC's

[Super_Blueberry]

I this is probably a dumb question that has been answered many times, but I can't seem to find a consistent answer. My general scenario is this: my 55 is heavily planted with ludwigia, swords, wisteria, crypts, dwarf sag, ricca, and my favorite Echinodorus vesuvius. I have 98 watts of t5 lighting, and I just started DIY co2 a few weeks ago. When I started the plants, I was doing 50% pwc's twice a week, and knocked that down to once a week with nitrates never getting above 20. Since I started the co2, my tap pH of 8.0 gets down to as low as 6.8 towards the end of the photo period (two 4-5 hour 'on' windows with a 4 hour 'off' window between, and an airstone on whenever the lights are off). Now when it comes to the pwc schedule I'd like to put them off as long as I can to eliminate as many ph swings as I can. Should I still do a weekly pwc? Or should I only do one when the nitrates get to 40? Should I just do smaller than 50% changes? From experience, what would all you experts recommend in my situation?

Thanks as always!

 

[ejaramillo01]

I experienced a similar scenario, but my pH was dropping from 7.4 to 6.7....
I was concern about the famous "pH swings", but looks like my fish did not care about it, so I kept doing weekly PWC (40%) with no problems...
Just my two cents.

 

[aqua_chem]

The general consensus about CO2-induced pH swings is they are a non-issue. In all honesty, I have seen little indication that pH is even a significant issue for most FW plants and animals beyond that fact that is is usually correlated with TDS and KH.

Also, if you had pressurized CO2, you pH wtould swing 1+ pH point every night, but no one ever sees an issue with that.

My rule of thumb is that you can never, ever hurt a FW tank with a PWC, assuming that everything else is taken care of (regular PWC, conditioner, temp).

Short answer: Don't sweat the pH.

 

[Super_Blueberry]

Short answer: Don't sweat the pH.

Perfect, thank you. What about the nitrate levels? My pwc schedule typically keeps them topped out at 10. Should I let them climb up to 30-40 for the plants and let that determine when a pwc is due? ...within reason obviously.