Adding buffer to newly mixed saltwater=precipitation?


Fish Freak
I am looking to do a pretty big water change today. I believe I have a big buildup of DOC in my water and for peace of mind I want to do a 50-75% water change.

Anyways I have a buddy who owns an aquarium maintenance company and he is going to help me with this. We mixed up a fresh batch of Salinity yesterday and I tested the alk today. It reads pretty low at 6.7dKH (I retested twice). My system is currently at 9.6dKH so obviously this big of a change is not good. I said we could just add buffer to the vat and he suggested against it. He stated to me that every time he has added buffer in the past to fresh salt that it would just precipitate out calcium and milk up the water. So my question is, what is the best way around this?

I know he just switched to Salinity recently and it has near NSW levels of calcium. The salt he used previously was Kent Marine which would read around 520ish in CA. Could that be the cause of his precipitation issue with adding buffer? Would we be safe bringing up dKH almost 3 points in newly mixed salt? How long should we wait to do the change after adding the buffer?

I know I can do smaller water changes frequently, I know massive water changes are advised against, im just looking to get a answer on the addition of buffer to newly mixed saltwater :)



-RT * ln(k)
The trick is to add the buffer very slowly just like you would in your tank. If you try to dump it in all at once it's going to precipitate for sure. Go slow and keep the water cold until you get the alkalinity up.


New member
Do you have a powerhead or anything in your saltwater mixing container? I've had unusual readings in my new mix as the solution would kind of separate. I've found running a power head before pulling water out for water changes have helped.

+1 on adding buffer slowly and with water motion. too much too fast and you'll see the precipitate coating the walls of the container.


Fish Freak
Its a 300 gallon vat with a Reeflo Barracuda attached :)


Thanks for the advise. We are going to premix baking soda into a gallon of RO and slowly drip it.


New member
Heres what I do.... I use Tropic Marine Pro and out of the bucket freshly mixed it tests ca-475 dkh-7.2 Mg-1275.... Being the ca is good I first dump 20oz mg and bring that up to 1350 I then SLOWY drip baked baking soda and bring the dkh up to 9 over night.
The idea of bringing mg up first is to stabilize the ca before adding the alk so nothing precipitates. Hth's