OK So I've been dosing SpongeExcel, although my test results don't seem to reflect the dose im calculating. I'll keep dosing until it gets to 2ppm SiO2.
Can I check though, I'm worried my Ph is climbing as I dose, it's normally rock solid at 8 but has crept up - I suspect due to dosing alkaline Silicate. Should I dose distilled white vinegar to compensate?
I'm going to order water glass as you recommend because this bottle of SpongeExcel wont last more than a week or two. I have a reefer 250 btw.
How much SpongeExcel are you dosing? I recommend dosing 2 ppm DAILY. For your tank and SpongeExcel that would be about 2 ml daily. How are you measuring silicon? None of the test kits we have in the States are helpful/accurate.
Best practice is to dose 2ppm/day and check an ICP in a few weeks to see where you are. Your are correct about it being very alkaline but at such small amounts I never saw it make a change in my pH. Unless your pH gets above 8.5 I wouldn't try to correct. White vinegar is a carbon source and will greatly fuel/worsen dinos!