Can anyone tell me if the sintered (I think that is the correct name)glass used in the Eheim filters absorbs lime? A tank has been set up with plenty of plants but no fish. The water is 7.0 pH out of the tap but moves up to 7.2 in the tank. The owner previously used the filter on an African set-up and was wondering if it had absorbed the lime used to raise the pH.

I've asked around and this is the response I got:

"I don't think a porous but essentially hard substance like sintered glass would absorb any significant quantity of lime. Lime would push the pH up to more than 7.2 probably.

A difference of 0.2 is almost too small to be measured by most aquarium kits - such a minor difference could be caused by lots of factors, such as the amount of aeration in the tank.

It may be worth testing (if they haven't already) the pH of the water straight from the tap, and after standing overnight, to see if there is a difference - the release of dissolved gases could account for the difference."

I hope it helps

We are aware it is not a big difference and a lot of other factors are involved. We just got curious about whether the media did actually absorb anything in that way. As you say, it is not a big difference, nor a problem.

Thanks for the reply. It obviously got you, and those you asked, thinking and discussing the subject

Hi Caryl,

I have useda lot of this type of media in one form or another for a very long time. I have done a lot of research into its structure. It is possible the media can abosorb lime if it is in powdered (particle) form. If it is disolved (as lime does actually dissolve a little in water) it will not stay in the media. If it is small undissolved particles it could quite easily get stuck inside the media pores. It will tend to dissolve back out very slowly over a period of time. The amount of leaching would be very small however. It is likely other factors are effecting the pH. If a large amount of lime is stuck in the media it will probably have clogged it and seriously reduce its biological performance.

The media's current state will depend on the type of lime (dissolved or powdered) added to the system and whether any of the lime precipitated out after being added.