How much did the P jump back up today? The rock/sand will unbind a bunch of P to "equilibrium" and the water level will rise again. This up and down "bounce" is what you are looking to avoid. Test it today and see. I would not be shocked if it is back up to 1.02, or so.
The best action is to use a very small amount of GFO and change it out quite regularly, like every day. This way, the rock/sand (aragonie) can unbind at about the same rate that you are removing it from the water column and you get no "up/down spikes." This will take a while.
GFO is quite safe to use, but if you use it too fast, or use too much, then you can really harm corals after a while.
If your tank is large at all, it could take many gallons of GFO to get your levels down below .1, for example. If you have a sump with filter socks, then you might consider some Lan Chloride since it is much cheaper and easier to dose. Once your levels get lower, then use some GFO to polish the water to where you want it to be - Lan Chloride works best in higher concentrations of P rather than lower.
Whatever you do, GO SLOW.
*I took over a reef with very old Marshall Island live rock (worth saving), a few clams, some easier SPS and a whole bunch of Z&P. P was about 1.0 and there was no algae since it was getting poisoned by the P - no coralline or soft algae. I used Lan Chloride into a sock for about 6-8 weeks to lower the P from 1.0 to about .15, then put some chaeto online (since it would grow now) and used a bit of GFO. I did a big water change once the P got lower - mostly to introduce trace elements back for the chaeto. Chaeto could keep the levels from rising, but cannot drop them, so that is why I used some GFO. Got the levels down to about .05, showed the owner how to test, prune the chaeto and even use some GFO if needed and have not been back. Reef is still doing good and growth has started again. I estimate that this would take about 5 gallons of GFO to get this 240g down this low. Coralline is growing strong again, but there were some times when hair, cyano and a few diatoms started to come when the P level got lower, but we pushed through.
I also use LC to remove P from used rock that I buy/trade since people getting rid of it have never taken care of it. It works great if you can remove the crystalline structure that it creates when it binds with the P (called floculant) - filter socks and/or HEAVY skimming work best.
