Temporary high phosphates for SPS?

[Reef Pilot]

I have 2 tanks running on separate sumps. But I have only 1 chiller. Last summer, I ran both tanks off the single sump with the chiller, and no problems. I would like to do the same again this year.

In the sump for the main display tank, I run both bio pellets and GFO, so my nitrates and phosphates are consistently zero. I have neither in the downstairs tank, and my nitrates run around 20 ppm while my phosphates are closer to about 0.6 at this point in time. Just a month ago the phospates in the downstairs tank were close to 1.0. But I switched my GFO to that sump, which brought down the phosphates. However, they are still a long ways from zero. Interestingly, the main display tank only has bio pellets now, and the phosphates are still staying at zero.

The concern is that I now have SPS in my main display tank, and they are used to zero nitrates and zero phosphates. If I combine the tanks into 1 sump, I expect the phosphates to go up considerably, maybe over .30, at least for a temporary time until the GFO can bring them down to near zero again. My SPS are doing really nicely now, with great color (eg. my purple cross is really purple), and I would hate to see them go brown, or lose their color.

So my question is, what do you think will happen to my SPS when I combine the tanks? I should mention that the main display tank with the SPS is 100 g, while the downstairs tank with LPS and softies is 130 g.

The other option is holding off combining them until the GFO brings down the phosphates a little more. But we have some warm weather in the forecast for later this week, and I know I will be fighting high temps in the downstairs tank. We had a warm spell back in April here, and the temps went up to 81 during the day time for a couple days. Normal temp is 78.

Of course, I should have started the GFO earlier on the downstairs tank. So now my choice is to live with higher temps in that tank during the warm spell, or higher phosphates for a while in my SPS tank.

What would you do?