The brown in the leaf is narcosis (dead plant tissue). This is the primary symptom of nutrient deficiency. Plant nutrients come in two basic varieties, Mobile and immobile:
Mobile nutrients can be removed from old leaves and moved to support new growth. The old leave eventually die and fall off. Mobile nutrients are nitrogen, potassium, Magnesium, phosphate, chlorine, molybdenum, and nickel.
Immobile nutrients cannot be moved by the plant. So new growth is affected strongly and older growth is also affected. Immobile nutrients are Calcium, Sulfur, Iron manganese, boron, zinc and copper.
I cannot be sure based on your picture but the poblem is likely an immobile nutrient. So fertilizing with a good micro should help. I would not trim the leave until the nutrient deficiencies corrected. if the deficiency is not corrected and you trim the leaves the plant may never recover and may die.
Note many micro fertilizers use sulfate ingredients manganese sulfate, zinc sulfate, and copper sulfate. These ingredients will react with carbonates in your water (KH) creating insoluble micro carbonates. Nutrients must be soluble for plants to use them. If you have KH in the water and are using sulfate micro fertilizer you need to dose about once every day or every other day. And for best results the water should be acidic about 6.5 with a zero KHfor best results. With acidic water and no KH one dose per week is fine.
I believe iron will help a plant maintain reddish leaves.
An Iron deficiency would cause the veins of the leaf to stay green while the rest of the leaf turns yellow. I don't see this in the picture. Not iron is particularly had to keep soluble in water. So most fertilizers use Iron gluconate or iron EDTA. Iron gluconate last one day in the water, Iron EDTA works best in with with a PH of less than 6.5. The insoluble byproduct of there decay can react iwht Phosphate resulting in insoluble Iron phosphate which plants cannot use. The bet iron ingredient is Iron DTPA it is stable up to a PH of 7.5 and may work up to a PH of 8. It is seldom used because it cost a bit more. But a single dose per week of Iron DTPA to a level 0.1ppm is sufficient in in most aqaureiums. So over the long term Iron DTPA will cost less of the user because a lower dose can be used.
Note phosphate and iron test kits cannot tell the difference between soluble and insoluble iron and phosphate. resulting in a phosphate and or a iron deficiency.
Also some plant are red naturally in the wild and in an aquarium. Others like red root floaters have green leaves in the wild but in many aquarium will have read leaves. I have determined that the primary cause of this is a soluble phosphate deficiency cause by iron gluconate or Iron EDTA. A soluble phosphate deficiency will prevent full development of chlorophyll allowing red pigments in the leaves to become visible.