Phosguard

[waynecav]

Does phosguard alter alkalinity levels? I use Phosguard, Matrix Carbon and Purigen in the external filter on my marine tank (all other media has been removed). I changed my phosguard on my last water change, my alkalinity was at 10.2 dkh, within 3 days it had dropped to 8 dkh.
I have plenty of surface movement for driving off co2, and I also run a skimmer rated well above my tank volume.
The only products I use on my tank are Seachem:

Seachem Reef Salt
Purigen
Phosguard
Matrix Carbon
Reef Trace
Reef Plus
Reef Buffer
Reef Adv Calcium
Reef Adv Magnesium

I mix my salt with RO water, heated and aerated over 24 hours to an SG of 30ppt.

[Tech Support EH]

PhosGuard does not directly alter alkalinity levels. However, you may notice an indirect connection between adding PhosGuard and KH. Phosphate itself acts as a buffer in water. Lowering the amount of phosphates in your tank will indirectly affect the alkalinity levels. Obviously, because PhosGuard works to remove phosphates, you may notice a slight drop in alkalinity initially. However, since you are buffering your water with Reef Buffer(a blend of carbonate and bicarbonate buffers), you should have no trouble adjusting the alkalinity back up.