I have samples of periphyton that I've scrubbed from rocks. I am trying to filter them and my filtration manifold is a Millipore 1225 sampling manifold (it looks like a blue barrel with 12 filtration ports). The problem is that the filter support has a spiral pattern and when my samples are drawn through my filter, the periphyton and sediment settle on the filter in the pattern of the spiral instead of getting even coverage. I have tried lowering the vacuum suction strength. That does not change the result. I have also tried putting qualitative paper (whatman 1) under the filters as extra support. That prevents the spiral pattern for the most part but it causes the filters to stay wetter (even with extended time) since there are 2 filters in place and it still has a thicker amount of periphyton/sediment around the outer edges. Has anyone else had a similar problem and if so, did you find a successful remedy? I've attached a picture of the filter with the spiral pattern.
If you are trying to enumerate/quantify the scrapped sample, the filtering method is perhaps not a very good approach because one would seldom get an "even" distribution of sample by using a filtering system of any sort. My experience is that as long as your sample is not dominated by filamentous algae (particularly blue-greens), it is perhaps better to use the Utermohl method to settle the sample into a chamber and enumerate it using an inverted microscope.??
When I use that filter housing I am usually trying to get as much algae on it as I can - so I usually use a spare filter to measure how much I can put on it without clogging it. It sounds like you want even coverage of microscopic observation. In that case you may have solved the problem with the filter paper supporting your sample-catching filter. What you may do after you filter is move the filter with your sample onto some blotting paper or a dry support filter to wick the extra moisture away so you can then proceed.
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