You can still use the canister just fill it with LR
rubble rather than filter media.
It sounds to me like you are using tap water not RO
. To really get control of the algae you need to have a good foundation and your water is that foundation. RO
units can be gotten on Ebay for about $100 and are well worth the investment. They remove pretty much everything from your water making it dang near pure.
If you can't get a unit right away check with your LFS
to see if they sell RO
Also feeding your tank, if you are feeding frequently and a lot of food this can contribute to increased nutrients in the water. You may want to reduce feedings to every other day and reduce the amount of food you feed. If you are feeding any frozen foods you will want to thaw them out and rinse them with RO
water to remove any excess nutrients before feeding the tank.