I am using large amounts of Rowaphos to reduce the phosphate quickly in my aquarium and noticed my KH drop, is this normal?
Rowaphos is a very effective phosphate remover so we would not recommend using excess amounts in one go. Always use about the recomended amount on the tub.
There are a couple of reasons or this
1. If you have high PO4 and reduce it quickly you can shock corals. This is because the zooxanthellae in the corals tissues will be acclimated to the higher nutrient values. A sudden drop in PO4 can cause issues such as bleaching or stripping. It is better to use the stated amounts and gently lower the PO4 levels over the coming weeks allowing the product to pull out as much PO4 as it can and then changing it out. Eventually you will bring the PO4 down to correct levels and you will be able to maintain it there with the correct use of Rowaphos.
2. Phosphate has a very similar effect to that of Magnesium in that it can prevent cascade precipitation of calcium carbonate. If you over dose Rowaphos and pull down PO4 rapidly you may find that Calcium and Alkalinity will start to precipitate locally at the media surface and you will see a drop in Alkalinity in the aquarium, this will be made all the worse if your Magnesium is also low. The precipitant will also start to block the media surface causing the media to lose efficacy quite quickly and potentially start to clump making it difficult to fluidise. As a result, you will not get the most out of the Rowaphos.