I would guess that you are having issues with N/P/K levels. (Nitrogen/Phosphorous/Potassium)

Are you fertilising much ? What are the N/P/K levels in your fertiliser ? Where on the plants are the leaves turning yellow ? On the bottom ?

If the lower leaves are yellowing and it is moving up the plant you might have a nitrogen deficiency, add some ferts high in nitrogen.

If you have a phosphorous problem your bottom leaves will also yellow and die, however, the small leaves will be a dark green. Growth will be stunted and slow. Add more P to feeding.

A potassium deficiency will show up as yellowing leaves on the bottom but it will also have spots on the leaves. Add more K to feeding.

So, if you are sure you arent over fertilising then use the above remedies.

However, you mentioned that some of the leaves were browning. this could be a sign of over fertilising.

If this is the case you need to flush the soil with water. If you can then check the PH of the soil in case it is too acidic as this will lock out nutrients to the plant. This then can look like a

deficiency but adding more fertiliser can simply do more damage.

So I'll leave it with you on what you wish to do, add more fertiliser or flush the pots thoroughly with distilled water to try to wash out the abundance of fertiliser, if you think its there.

Take Care

S.L.