Low alk on all my tanks

[Montipora840]

Hi guys, I'm kind of at a loss. I have a 38g reef with a 20g sump, a 55g sumpless FOWLR tank, and 10g mantis tank.
For some reason, every tank eats up alk like theres no tomorrow, I'm talking around 6dkh and it drops the ph to about 7.7-7.8 too. On the reef alone I have to dose 5.25 ML of reef buffer every day to keep it level. There is no way I should be having to dose like this is there? When I first noticed the problem I thought it was just the PH, so I tried opening the window and putting in a fan thinking it might be built up Co2 in my room, that didn't do anything, I even put an air pump outside my window and had it pumping fresh air through an airstone into my sump, still did nothing.
If anyone has any ideas that would be great, thank you for your time.

[shred5]

Biological activity will use up alk. Do you have a deep sand bed? Do you do carbon dosing of any type? These types of tanks can use alk up faster.

[Montipora840]

Sand bed is about 3-4" in the reef and no I don't. That's just the reef though, every one of my tanks is doing this. My 55g fowlr is bear bottom, and the mantis tank has a DSB. I just don't think I have heard of anyone having to dose this much every single day.

[shred5]

How is your magnesium levels? If you have low magnesium levels and high calcium it will push down alk.

[Montipora840]

Last time I checked they were great, and my ca has been sitting at about 420-440 in the reef the whole time, literally the only problems I have found were alk and ph. One of the reasons I'm so confused lol.

[dsmhero]

Well alk and Ph go hand in hand. I dose 3ml of alk 2part each day and that is with a lightly stocked 24g, so I do not think 5.25ml is very much to dose. I agree with double checking your mag but using up alk is a usually good sign in a tank.

[Surf&turf]

I dose 3 oz. of alk 2part each day in a 90.