hi have the fake plastic plants in my 20 galloon tank, may sound stupid but i find it hard to keep the plants from staying on the bottom of the tank, i cover the base of the plants with gravel and some still rise to the top any suggestions, can i tie something to the bottom of the plantbase to make sure they stay at the bottom it is a pain after cleaing the tank having to rearrange the tank and find it difficult to make the plants stay at the bottom. any suggestions thanks?