No, no, you’ve got the wrong end of the stick! It’s not some horrible problem at all, but to do with aquariums.
Marine aquariums need bio-filtration, and this is provided by bacteria. The bacteria of course need a place to live and to avail oneself of this free service from nature the aquarist must provide them with a suitable home.
The bacteria operate what is called the Nitrogen Cycle, either fully or in part. To operate in part is easy, all that is required is plenty of oxygen plus ammonia and then nitrite. The bacteria will change the ammonia to nitrite, and then the nitrite will be changed to nitrate. Ammonia and nitrite are toxic, and nitrate much less so.
To support livestock it is enough to do only as in the previous paragraph. The toxic ammonia and nitrite are dealt with. Nitrate is left and this should not harm anything at very low levels.
However, the levels will slowly increase beyond the guideline (for a reef system) which is 10ppm (parts per million) or less. One way of reducing the level is with routine seawater changes. These changes are good for other reasons and should be completed, however nitrate could increase in spite of them. Nitrate increases are not desirable as the appearance of nuisance algae may occur.
Nature has a remedy but it cannot occur where there is oxygen present in any normal amount. The bacteria that reduce nitrate need an environment that is very low in oxygen – this forces the bacteria to extract oxygen from the nitrate thus removing it (it converts to gas and escapes the aquarium).
So bio-balls are a good medium for oxygen hungry bacteria, but not for bacteria that deal with nitrate.
If nature is going to assist with nitrate reduction, a denitrator (a so-called nitrate ’reactor’) could be used. Better, live rock can be used. Live rock has surfaces that can be used by oxygen needing bacteria, and well inside are areas for the nitrate bacteria. Live rock with a DSB (deep sand bed) is even better.
So if an aquarist is using bio-balls the answer is yes, it will be all right, except that the bacteria will produce nitrate and that will be the end of nature’s assistance.
If bio-balls are in use in addition to sufficient live rock (and perhaps a DSB) then the bio-balls can be removed, but remove them a few at a time over a period of weeks. This will allow any bio-load that was supported by the balls to be taken up gradually by the other media.
If the bio-balls were the only media, then none must be removed straightaway. Introduce sufficient live rock into the aquarium, wait a week or two, then commence removing the bio-balls a few at a time as already described. It would be of little use introducing, say, a canister filter for bio-filtration as the end product is the same – nitrate.
A good few years ago bio-filtration methods included balls. Times have changed.