Diatomaceous earth filters use a powder that attaches itself onto a filter grid inside the filter. When the filter grid becomes damaged the diatomaceous earth powder can go through the filter and back out the return jet. This leaves your pool a cloudy, muddy-looking mess. Luckily however, the powder usually sinks to the bottom of the pool. The only way to remove the earth from your pool is to vacuum the pool with the filter release valve open. This will allow the earth to flush from the filter.
Turn the filter off and allow the earth to settle to the bottom of the pool. Most of it will sink to the bottom but with the filter on you run the risk of recirculating the earth which will make the water even more cloudy.
Connect the pool hose to the vacuum assembly and drop it in the pool. Connect the opposite end of the pool hose into the pool skimmer. Pump the filter handle three to five times to build up filter pressure for the vacuum.
Connect another pool hose from the release valve opening located near the bottom of the pool. Lead this hose into, or in the direction of, the nearest drain in your backyard. When you vacuum, the water will be coming out from this opening. You will lose a lot of pool water during this procedure but it's the only way to ensure you get the diatomaceous earth from the pool bottom.
Turn the release valve port to the backwash setting. Turn on the filter. Begin to vacuum the pool slowly. The faster you move the vacuum through the water the more chance you have of kicking the dirt up. You may need to vacuum the pool in increments, allowing the diatomaceous earth to settle each time until it is all eventually gone or the possibility of flooding becomes an issue.