Mg too low / high

Magnesium is an essential mobile plant nutrient and must be supplied by tap water, fertilizer or substrate. Generally plants take more of Mg then they need and store it for later use. Interestingly enough, Mg is not supplied as NO3 and PO4 by fish waste and plant decay.

FAQ

What happens if there is Mg deficiency?

Plants slow down grow rate and develop pale older leaves.

What is the usual water column Mg level?

See Plant requirements

What is the lowest Mg levels I can have with plants?

Mg levels in fully planted aquariums can drop to zero during a day. If there is daily supply by PPS dosing nothing happens. But uninterrupted zero levels for several weeks may stunt plant growth and recovery can take a long time.

How can I increase Mg levels?

Dose more of fertilizer or use Dolomite as substrate. Please see RO Reverse Osmosis for more details.

How much of Mg fully planted aquarium needs?

Daily about 0.1 ppm. More can be also utilized but in the long run plants will get saturated and will not take more.

I have heard about much higher Mg levels?

Some tap water comes with higher Mg levels naturally. Unfortunately high KH follows and most plants and fish don’t do well in high KH water.

What happens if there is Mg excess?

Some plants and fish don’t mind relatively high levels but some do, it does depend on particular specie.

Can fish die from high Mg levels?

I have not heard of such a problem.

How can I lower Mg levels?

Check fertilizer. Check water supply for Mg excess. Check decorations, rocks and substrate. Switch from tap to RO Reverse Osmosis filter.