Outrageously high alk with no dosing

[altolamprologus]

I tested my alk today to make sure my GFO wasn't stripping too much out of the water and the result surprised me. It's 16 dkh!! I even tested again (using a salifert test kit both times) and got the same result. Then I tested the natural seawater I use for water changes and it's at the expected 8 dkh. The tank is mostly filled with macro algae and about a dozen non-photosynthetic corals and gorgonians. I've never dosed alk, but I do dose iodine, iron chelate, potassium nitrate, and large amounts of phyto feast live and other filter feeding foods. Could the alk be coming from the phyto feast? Or something else?

[bertoni]

The alkalinity might be coming from the salt mix, any tap water added to the tank, or pH buffers. The food products won't add any alkalinity. Have you tested any freshly-mixed saltwater?

[altolamprologus]

The alkalinity might be coming from the salt mix, any tap water added to the tank, or pH buffers. The food products won't add any alkalinity. Have you tested any freshly-mixed saltwater?

I never use tap water, only 0 TDS RO/DI and I have never used a PH buffer or any alk supplement on this tank. Also, I don't use a salt mix for this tank, just natural seawater with a dkh of 8.

[bertoni]

Hmm, what is the iron chelate? I guess that's too small a supplement amount to make a difference, though. I have no idea where the tank might be getting the alkalinity.

[dartier]

What about the substrate and rock? Is the rock natural or man made? If man made I am wondering if it could be raising the alkalinity?

Dennis

[bertoni]

Good catch! Artificial live rock does have that effect sometimes.

[altolamprologus]

The iron chelate is a liquid iron supplement from gulf coast ecosystems. I dose just a couple mls a week of that though.

The rock is all natural, as is the sand. The tank had been running for over a year with no new rock or sand and has never had alk issues. I've only tested a few times since the only corals are non-photosynthetic, and it has never gone above 9 dkh, and it was only that high when I used a reef salt mix.

Does anyone think it would be a good idea to dose some calcium to get it more in balance? Or should just do large water changes and try to correct the alk and not worry about calcium and magnesium?

[Buzz1329]

"I tested my alk today to make sure my GFO wasn't stripping too much out of the water . . . "

Non sequitur. What makes you think that GFO will "strip" alkalinity from the water?

[bertoni]

I have no idea what the source of the alkalinity is. It'd take a very strangely-made food to have much alkalinity in it.

[altolamprologus]

"I tested my alk today to make sure my GFO wasn't stripping too much out of the water . . . "

Non sequitur. What makes you think that GFO will "strip" alkalinity from the water?

Look up advanced aquarist's article "Aquarium Chemistry: Effects of GFO (Granular Ferric Oxide) on 'Trace' Metals Concentrations in Artificial Seawater". GFO removes some alkalinity from the water and since I use quite a large amount of GFO, I wanted to make sure it wasn't removing too much.

[bertoni]

Yes, GFO sometimes remove alkalinity and calcium from the water, by encouraging precipitation. In some cases, the GFO has noticeable white blotches in it after use.

[altolamprologus]

I have no idea what the source of the alkalinity is. It'd take a very strangely-made food to have much alkalinity in it.

I'm starting to think it might be the phyto because I use massive amount of it (about 40 ounces a month), and one of the ingredients is saltwater (obviously). I keep salinity in check by removing small amount of tank water and replacing it with RODI, but maybe that's not enough to combat the extra alk? Idk for sure, it's just what I can come up with at the moment. I might mix some with RO and text alk to see if that's a possibility.