Above you can see some pictures of the dye in use, the stronger the dose the more coloured the water will become, even if you were to overdose by 10 times there is still no harmful affects on aquatic life such as fish and invertebrates, it only blocks out some of the light spectrum starving vegetation, marginal and surface plants are not affected. If treating weed ideally the dye needs to be added in early spring before the weed gets going, at the minimum dose the dye will have cut out enough of the light spectrum at a depth of 60cm to prevent weed growth, if you double the dose the dye will have blocked out the light at a depth of about 30cm.
With algae it works in a slightly different way, at the minimum dose rate the dye has blocked out enough of the light spectrum below 60cm so the algae cannot survive in the lower layers, this reduces the total volume of water the algae can survive in, thus reducing the overall amount of algae present in the water body.
Algae floats about in the water column and can migrate to the surface so with algae it is best to keep the lake at a higher dose rate, from personal experience (depending how severe the algae problems are) i would recommend double the minimum dose rate, this then has to be kept topped up. Even at double the standard dose rate there will still be some algae in the system, low amounts of algae are beneficial as it provides food for rotifers and zooplankton that are then consumed by the fish, but when algae gets out of control it can cause huge problems from massive dissolved oxygen and ph swings to total de-oxygenation if it suddenly dies back.