Originally Posted by Anchorhandler
A dip slide test will show bacterial percentage and allow you to see just how bad your fuel is.
Even if you've never performed a test before, a dip slide can be compared to a reference chart ( included with the test) which will show how bad the contamination actually is.
Incubation period is usually 24-48 hours after the slide is replaced in its sealed container.
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Simon, I really do know what I am talking about! I'd hazard a guess I've done more dipslides than you've helmed tugs.
- Dipslides don't measure "bacterial percentage"
- A displide for a fuel tank should not only be measuring bacteria (as its generally regarded that the biggest problems are fungal)
- Displides are sensitive to their incubation conditions. If you leave them 48 hours in an airing cupboard you'll get different results from if you leave them in a proper controlled incubator. The former can be ok as an indicator of changes from time to time - but without proper control gives little information on a specific site.
- All microbiological procedures are very sensitive to sampling technique. You've got 400+ L of fuel, and are going to sample 0.1 mL (typically) so will be looking at a 1 in four million snap shot of the system. If its high / low how sure would you be that the whole system is/isn't a problem.
- Its almost inevitable that something will grow on the slide, if you leave it long enough, with fuel thats been in those sort of storage conditions. So you need a rational approach to how you are going to deal with the growth you see - willk's already planning to clean/polish anyway. You'd want to follow up to be sure any treatment has been effective, and as it only takes one spore somewhere in the system (almost impossible to remove) to reseed the system - so you need to keep an eye on it.
- I've never done a quality comparison on fuel displides but I have looked at variability on those used in water testing - and there is essentially little standardisation, so (i) depending which media is used, (ii) depending on the manufacturer (many are made by the same factory and just labelled), (iii) the age, shipping and storage conditions of the slide can all impact on performance.
- All dipslides are selective (to varying extents) for what they grow, its very likely that if you get half a dozen colonies of the target organisms growing that you have a whole load of other stuff in there too.
I'm not suggesting dip slides are not a useful tool for monitoring tanks - but a single test result tells you very little. If he cleans his tank and is still worried then running a dipslide as part of the routine maintenance and keeping a track of the trend would be far more use and early warning of growth than a single data point before he goes and disturbs the whole system. I know Willk has a scientific bent deep down and will get the point I am making.