is it loose clumping or hard clumping? loose clumping is usually from sticky biofilms from excess dissolved organics,hard clumps is usually calcium carbonate binding

Another good way to tell why its clumping is to put the clump into some bleach water, if it falls apart its excessive organics if vinegar is the only thing that breaks it apart its calcium

If it is precipitated calcium, then 10 bucks says your magnesium is less then 1300 ppm.:wink:

What are your calcium, alkalinity, and magneisum levels?

Are you using Kalk to support Ca/Alk? That clumping can easily occur with heavy Kalk dosing.

Reasoning being:

-kalk spikes the ph which can make precipitation happen easier
-kalk use often leads to depleted magnesium levels

I would keep your magnesium at 1400ppm or so.:wink:

Not adding kalk, but using a cal reactor. Cal=400, Alk= 11, don't know mag.
It breaks apart when taped but if just moved around it stays together, the tank has only been running for 2 months.

What salt?

Io

What I figured.

IO works very good for fish only.

I use it for my reef, and so do many others. For myself I found it very hard to keep my alk and calcium in-line, untill I started adding magnesium to the mix.

FWIW it takes a lot of magnesium to get it to where you want it.

Many people follow my home made recipe:

Just do the math to get it to follow your water change shed:

-45 gallon of new water (RO, or DI or RO/DI)
-add 1.5 cups of magnesium
-add 6 teaspoons of calcium
-after the cal and mag are mixxed add the salt.

This will yield app 1380 mag, 420 cal, and 10 dkh alk

I always recommend testing, but FWIW I have not tested magnesium for over 3 years, and things are still going great for my tank, no precip on my pumps, or anywhere else!