Ntlabs oxygen test kit for pondsr oxygen is essential for the fish plants and filter bacteriar the concentration of dissolved oxygen in the water can drop to dangerous levels causing hypoxia stressr the most accurate oxygen test kit on the market for a healthy pond and fish oxygen o2 levels must be high cold water carries a lot more o2 so this is less of a concern in winter monthsr test regularly in summer months when the temperature rises and o2 levels drop especially in humid conditi